A pump body assembly, comprising: an oil supply passage configured for circulating oil; two back pressure members, the two back pressure members are an upper flange and a lower flange respectively; wherein an end face, facing the upper flange, of the lower flange is provided with a back pressure groove, the back pressure groove comprises a first groove section and a second groove section, the first groove section and the second groove section are disposed at intervals, the first groove section is communicated with the oil supply passage, and the second groove section is communicated with the oil supply passage; a communication area of the first groove section and the oil supply passage is a, and a communication area of the second groove section and the oil supply passage is b, and a < b; wherein the pump body assembly further comprises a rotary shaft which passes through the two back pressure members, characterized in that, the oil supply passage comprises a flow passage disposed in the lower flange, wherein the flow passage comprises a first flow passage and a second flow passage, the first flow passage is communicated with the first groove section, and the second flow passage is communicated with the second groove section; wherein an area of a first opening, communicated with the first groove section, of the first flow passage is a, and an area of a second opening, communicated with the second groove section, of the second flow passage is b; wherein the oil supply passage further comprises: an oil passage disposed on the rotary shaft, wherein the oil passage is communicated with the first flow passage and the oil passage is communicated with the second flow passage; an oil cavity provided on the lower flange, wherein the oil cavity is communicated with the oil passage and the oil cavity is communicated with the flow passage so that the oil passage is communicated with the first flow passage through the oil cavity, and the oil passage is communicated with the second flow passage through the oil cavity; wherein the flow passage is disposed between the oil cavity and the back pressure groove. an oil supply passage configured for circulating oil; two back pressure members, the two back pressure members are an upper flange and a lower flange respectively; wherein an end face, facing the upper flange, of the lower flange is provided with a back pressure groove, the back pressure groove comprises a first groove section and a second groove section, the first groove section and the second groove section are disposed at intervals, the first groove section is communicated with the oil supply passage, and the second groove section is communicated with the oil supply passage; a communication area of the first groove section and the oil supply passage is a, and a communication area of the second groove section and the oil supply passage is b, and a < b; wherein the pump body assembly further comprises a rotary shaft which passes through the two back pressure members, characterized in that, the oil supply passage comprises a flow passage disposed in the lower flange, wherein the flow passage comprises a first flow passage and a second flow passage, the first flow passage is communicated with the first groove section, and the second flow passage is communicated with the second groove section; wherein an area of a first opening, communicated with the first groove section, of the first flow passage is a, and an area of a second opening, communicated with the second groove section, of the second flow passage is b; wherein the oil supply passage further comprises: an oil passage disposed on the rotary shaft, wherein the oil passage is communicated with the first flow passage and the oil passage is communicated with the second flow passage; an oil cavity provided on the lower flange, wherein the oil cavity is communicated with the oil passage and the oil cavity is communicated with the flow passage so that the oil passage is communicated with the first flow passage through the oil cavity, and the oil passage is communicated with the second flow passage through the oil cavity; wherein the flow passage is disposed between the oil cavity and the back pressure groove. an oil passage disposed on the rotary shaft, wherein the oil passage is communicated with the first flow passage and the oil passage is communicated with the second flow passage; an oil cavity provided on the lower flange, wherein the oil cavity is communicated with the oil passage and the oil cavity is communicated with the flow passage so that the oil passage is communicated with the first flow passage through the oil cavity, and the oil passage is communicated with the second flow passage through the oil cavity; wherein the flow passage is disposed between the oil cavity and the back pressure groove.