The present invention discloses an inter-frame predictive coding method and a coder. Inter-frame predictive coding is sequentially performed on frames in multiple groups of pictures by using a group of pictures as a unit; a correlation between the reference B frame and a GPB frame in the same group of pictures is used; and when the maximum depth of the CTU in the same position in the GPB frame is smaller, a quantity of mode decisions performed on the CTU in the reference B frame may be relatively small, so that an objective of reducing complexity of an inter-frame predictive coding process of the reference B frame is achieved.