A breaststroke leg strength training device, including a lower panel, and a prostrate platform connected with the panel through an elastic band and located below one side of the panel; a slit consistent with a breaststroke leg movement trajectory is formed in the panel, and an elastic band attachment column is respectively arranged at positions on both sides of the slit and on the panel; two foot pedal middle shafts are arranged in the slit and extend to the lower side of the panel; and the elastic band is connected with the attachment columns through a fixed beam fixed to the platform and the two foot pedal middle shafts. The device has a smart structural design, a trainer can comprehensively train all the muscle groups involved in the breaststroke leg actions in a continuous and efficient manner, and the breaststroke leg actions of the trainer can be specified and corrected.