In most of video coding standards such as high efficiency video coding (HEVC), I-frame assignment is periodic even when the content change is minor, which degrades the coding efficiency. This paper proposes an I-frame assignment method based on Nash bargaining solution (NBS) in game theory to solve this problem. The encoded sequence is divided into several subsequences. Each subsequence is regarded as a game. All group of picture (GOP) in a subsequence is further divided into several sets of GOP. Each set of GOP is regarded as a player and compete for the number of I-frames. The optimal I-frame assignment is determined based on the generalized NBS. Experimental results show the proposed method outperforms HEVC by 5.21% bitrate saving.