Embodiments of the present invention disclose a method, a device, and a system for self-adaptively adjusting a data transmission rate, which solve the problem of network buffer overflow. The method includes: receiving parameters sent by a client; calculating a predicted value of a data sending rate according to a maximum value of a network buffer and the received parameters; judging whether the predicted value of the data sending rate is less than an original service bit rate; and if the predicted value of the data sending rate is less than the original service bit rate, discarding data of at least one data unit in a send buffer. The method, the device, and the system are mainly applied to adjust the data transmission rate, and especially to adjust the data transmission rate in a time-varying network.