A mechanism for mixing a supercritical fluid and a polymer raw material melt, comprising: a hot-melting unit, having a hollow pressing cartridge, wherein a first feeding passage and a first discharging passage are disposed at two ends of the pressing cartridge, respectively, and communicate with a hollow interior of the pressing cartridge and the external space of the pressing cartridge, respectively; a pushing member is disposed in the pressing cartridge between the first feeding passage and the first discharging passage, and is used to push, toward the first discharging passage, a polymer raw material entering the hollow interior of the pressing cartridge through the first feeding passage; a mixing unit, having a hollow mixing cartridge, wherein a second feeding passage and a second discharging passage are disposed at two ends of the mixing cartridge, respectively, and the second feeding passage communicates with the first discharging passage, such that the polymer raw material pushed out of the first discharging passage enters a hollow interior of the mixing cartridge through the second feeding passage; a mixing rotor is disposed in the mixing cartridge between the second feeding passage and the second discharging passage, and is rotatable in the mixing cartridge, so as to agitate the polymer raw material accommodated in the mixing cartridge; a supercritical fluid supplying unit, disposed on the mixing unit and spaced from the hot-melting unit, such that the external supercritical fluid is introduced into the hollow interior of the mixing cartridge, and together with the polymer raw material in the mixing cartridge, is agitated by the mixing rotor and mixed into a homogenous single-phase solution, wherein the supercritical fluid supplying unit has a gas transfer passage, disposed on the mixing cartridge and communicating with the hollow interior of the mixing cartridge, and used to form a flow passage through which the external supercritical fluid enters the mixing cartridge, wherein the gas transfer passage is disposed adjacent to the second feeding passage, wherein the mixing rotor has a column-like body, rotatably disposed in the mixing cartridge; a first groove portion is annularly arranged on the periphery of the column-like body and a second groove portion is annularly arranged on the periphery of the column-like body characterised in that the first groove portion is arranged at one end of the column-like body adjacent to the second feeding passage and is adjacent to the second feeding passage and the gas transfer passage, and the second groove portion is arranged at the other end of the column-like body adjacent to the second discharging passage, wherein the first groove portion and the second groove portion are arc-shaped portions of different curvatures, and wherein the second groove portion consists of two intersecting arc-shaped portions. a hot-melting unit, having a hollow pressing cartridge, wherein a first feeding passage and a first discharging passage are disposed at two ends of the pressing cartridge, respectively, and communicate with a hollow interior of the pressing cartridge and the external space of the pressing cartridge, respectively; a pushing member is disposed in the pressing cartridge between the first feeding passage and the first discharging passage, and is used to push, toward the first discharging passage, a polymer raw material entering the hollow interior of the pressing cartridge through the first feeding passage; a mixing unit, having a hollow mixing cartridge, wherein a second feeding passage and a second discharging passage are disposed at two ends of the mixing cartridge, respectively, and the second feeding passage communicates with the first discharging passage, such that the polymer raw material pushed out of the first discharging passage enters a hollow interior of the mixing cartridge through the second feeding passage; a mixing rotor is disposed in the mixing cartridge between the second feeding passage and the second discharging passage, and is rotatable in the mixing cartridge, so as to agitate the polymer raw material accommodated in the mixing cartridge; a supercritical fluid supplying unit, disposed on the mixing unit and spaced from the hot-melting unit, such that the external supercritical fluid is introduced into the hollow interior of the mixing cartridge, and together with the polymer raw material in the mixing cartridge, is agitated by the mixing rotor and mixed into a homogenous single-phase solution, wherein the supercritical fluid supplying unit has a gas transfer passage, disposed on the mixing cartridge and communicating with the hollow interior of the mixing cartridge, and used to form a flow passage through which the external supercritical fluid enters the mixing cartridge, wherein the gas transfer passage is disposed adjacent to the second feeding passage, wherein the mixing rotor has a column-like body, rotatably disposed in the mixing cartridge; a first groove portion is annularly arranged on the periphery of the column-like body and a second groove portion is annularly arranged on the periphery of the column-like body characterised in that the first groove portion is arranged at one end of the column-like body adjacent to the second feeding passage and is adjacent to the second feeding passage and the gas transfer passage, and the second groove portion is arranged at the other end of the column-like body adjacent to the second discharging passage, wherein the first groove portion and the second groove portion are arc-shaped portions of different curvatures, and wherein the second groove portion consists of two intersecting arc-shaped portions.