The invention discloses a motor and oil pump assembly, a steering system and a vehicle. The motor and oil pump assembly comprises a motor module, an inner sound-proof cover, an oil pump module and a pre-tightening buffering module. The oil pump module and the inner sound-proof cover define an inner sound-proof cavity filled with low-pressure oil. The inner sound-proof cavity communicates with a low-pressure cavity of the oil pump module. The pre-tightening buffering module comprises a piston and an elastic piece, wherein the piston is matched with a sound-proof cover cavity and abuts against the upper end cover of the oil pump module and stopped by the upper end cover, the elastic piece is elastically clamped between the bottom wall of the sound-proof cover cavity and the piston. The sound-proof cover cavity communicates with a high-pressure cavity of the oil pump module, so that the piston tightly presses the upper end cover under the action of oil pressure. An energy storage cavity is arranged on a high-pressure oil channel between the sound-proof cover cavity and the high-pressure cavity. The motor and oil pump assembly is high in lightening level, low in work noise, small in impulse fluctuation, stable in output and high in work energy efficiency.