This application relates to the field of communication technologies, and provides a method and an apparatus for updating a preprocessing parameter. A first apparatus performs preprocessing and power amplification on a first signal by using a first preprocessing parameter, to obtain a third signal; and then sends the third signal to a second apparatus, where the third signal is changed to a fourth signal after passing through a channel between the first apparatus and the second apparatus. The second apparatus performs channel estimation and channel equalization by using the fourth signal, to obtain a fifth signal, and then determines an updated preprocessing parameter based on the fifth signal. Next, the second apparatus indicates the updated preprocessing parameter to the first apparatus. Channel estimation and channel equalization can eliminate a linear part of the fourth signal. When the updated preprocessing parameter is estimated, only impact of a nonlinear part on the signal is considered, so that an optimal preprocessing parameter can be obtained more accurately, to implement accurate preprocessing and improve working efficiency of a communication device.