In CCPM Technique, as the buffer size calculation method, the Cut and Paste(C&P) method and the Root Square Error (RSE) method for all tasks carried out the same treatment, without considering the actual situation and characteristics of the task, the lack of reasonable judgment, is too simple and hasty. In this paper, taking into account the limitations of existing methods, a new method of buffer sizing method based on statistical analysis was introduced. It makes statistical analysis for the relationship between each worker and a variety of tasks, and use the information to predict the next task time. In order to verify the effectiveness of the new method, according to different task difficulty and the number of tasks set up the project. Use C&P, RSE method and new methods to predict the time of the project. Through Monte Carlo Simulation to simulate the project time, a comparison of three methods of performance. The results show that the new method can achieve the managers expect the probability of completion, and for those tasks can be completed ahead of schedule, the new method can save project time.