The invention relates to a medical instrument, in particular to a device for promoting uterine contraction by stimulating a nipple. The device comprises a flexible cup body capable of wrapping a breast, wherein a rigid outer cover supporting the cup body is arranged on the outer side of the flexible cup body, and a vibration assembly which can extend into the flexible cup body and stimulate the nipple is arranged on the rigid outer cover and is controlled to vibrate through a control device. By the aid of the vibration device, the nipple can be regularly stimulated to cause uterine contraction, postpartum lactation is enhanced, postpartum hemorrhage and postpartum pain are reduced, the vibration frequency of the device for promoting uterine contraction can be adjusted according to uterine contraction and tolerance of a parturient, and the clinic difficulty is solved.