Abstract: Taking 8 IGS station time series inside China as research object, this paper analyzes the law of non-linear variation. First, the periods of station time series are obtained by spectral analysis, finding that the annual non -linear variation is a common role, it is just different in amplitude of variation; other periodic items vary from station to station, and the periodic law in vertical direction is the most obvious. Then station time series are fitted by triangle method according to the periodical rule, the results show that it can exhibit the law of non-linear variation directly, which is beneficial to further analyze the property and mechanism of non-linear variation. The results would provide important reference for establishing and maintaining the high-precision terrestrial reference frame.