An oil pump, comprising: a shell having an inlet and an outlet and defining a low-pressure oil chamber and a high-pressure oil chamber therein, the low-pressure oil chamber having a low-pressure oil passage communicated with the inlet, the high-pressure oil chamber having a high-pressure oil passage communicated with the outlet; a rotor mounting part disposed at an end of the shell and having a rotor supporting structure; a rotor mechanism disposed on the rotor mounting part; and a flow limiting wall disposed in the buffer chamber, wherein the flow limiting wall divides the buffer chamber into an inflowing buffer chamber and an outflowing buffer chamber communicated with the inflowing buffer chamber via a pressure relief mechanism, wherein a barrier wall is disposed between the outflowing buffer chamber and the low-pressure oil chamber; wherein the high-pressure oil chamber and the low-pressure oil chamber are located at the same side of a periphery of the rotor mounting part side by side; wherein a buffer chamber is defined between the low-pressure oil chamber and the high-pressure oil chamber; wherein the buffer chamber, the high-pressure oil chamber and the low-pressure oil chamber are located at the same side of a periphery of the rotor mounting part side by side; characterized in that the shell comprises a main shell body and a cover jointed with the main shell body, the inlet and outlet formed in the cover, wherein the flow limiting wall comprises a first flow limiting wall portion formed on the cover, and a second flow limiting wall portion formed on the main shell body, and wherein a through hole communicating the inflowing buffer chamber and the outflowing buffer chamber is formed in the flow limiting wall, and the pressure relief mechanism is disposed in the through hole. a shell having an inlet and an outlet and defining a low-pressure oil chamber and a high-pressure oil chamber therein, the low-pressure oil chamber having a low-pressure oil passage communicated with the inlet, the high-pressure oil chamber having a high-pressure oil passage communicated with the outlet; a rotor mounting part disposed at an end of the shell and having a rotor supporting structure; a rotor mechanism disposed on the rotor mounting part; and a flow limiting wall disposed in the buffer chamber, wherein the flow limiting wall divides the buffer chamber into an inflowing buffer chamber and an outflowing buffer chamber communicated with the inflowing buffer chamber via a pressure relief mechanism, wherein a barrier wall is disposed between the outflowing buffer chamber and the low-pressure oil chamber; wherein the high-pressure oil chamber and the low-pressure oil chamber are located at the same side of a periphery of the rotor mounting part side by side; wherein a buffer chamber is defined between the low-pressure oil chamber and the high-pressure oil chamber; wherein the buffer chamber, the high-pressure oil chamber and the low-pressure oil chamber are located at the same side of a periphery of the rotor mounting part side by side; characterized in that the shell comprises a main shell body and a cover jointed with the main shell body, the inlet and outlet formed in the cover, wherein the flow limiting wall comprises a first flow limiting wall portion formed on the cover, and a second flow limiting wall portion formed on the main shell body, and wherein a through hole communicating the inflowing buffer chamber and the outflowing buffer chamber is formed in the flow limiting wall, and the pressure relief mechanism is disposed in the through hole.