Aimed at the insufficiency of the traditional trajectory prediction, an improved method of trajectory prediction based on subsection is given. First, the general method of trajectory prediction in free phase is introduced, the causes of trajectory prediction error are analyzed. Then an idea of subsection is put forward, which turns the prediction end point of the former part to the prediction start point of the next part for the purpose of reducing the accumulation of prediction error, in this way, the improved method of trajectory prediction is obtained. Finally, the relevant algorithms and processes are simulated and analyzed, the results show that this method is reasonable and effective in reducing the error of trajectory prediction.