A breast pump includes a main body (1), a breast milk suctioning shield (2), and one or more air pumps (4). The main body (1) has an accommodation space (11). The breast milk suctioning shield (2) is assembled in the accommodation space (11) and detachably connected to the main body (1). A front end of the breast milk suctioning shield (2) has a breast shielding portion (21), and a nipple passage (22) extends from a rear end of a center portion of the breast shielding portion (4). One or more deformable members (25) and a non-deformable supporting member (24) are assembled with an annular connection portion (23) located between the breast shielding portion (21) and the nipple passage (22). The air pump (4) has an intake port (41) and an exhaust port (42). The intake port (41) is controlled by a first valve controller (3) to suction the nipple passage (22) and generate a negative pressure, and the exhaust port (42) is controlled by a second valve (9) controller to inflate or deflate the deformable member (25).