The present disclosure relates to a breast pump comprising a suction mechanism and a main body. The suction mechanism comprises an elastic bowl and a suction assembly, the elastic bowl having an accommodation cavity and being at least partially accommodated in the suction assembly. The main body comprises a boss sealingly fitting with the accommodation cavity of the elastic bowl, the boss being provided with a suction hole that is in communication with the accommodation cavity to create a connected passageway. When the main body extracts air through the suction hole and the accommodation cavity decreases so that the elastic bowl contracts, there is no gap between the elastic bowl and the boss, and negative pressure is generated in the suction assembly.