An oil pump is provided. The oil pump comprises: a shell; a rotor mounting part on the shell and having a rotor supporting structure; and a rotor mechanism disposed on the rotor mounting part. The shell has an inlet and an outlet and defines a low-pressure oil chamber and a high-pressure oil chamber. A partition wall is disposed between the low-pressure oil chamber and the high-pressure oil chamber for separating the low-pressure oil chamber and the high-pressure oil chamber. An engine cover comprising the oil pump and an engine comprising the engine cover are also provided.