Abstract: The classical study of critical chain buffer determination assumes that the activity can only be started immediately after the preceding activity is completed, without considering the influence of different precedence relations on buffer determination. In order to determine the reasonable and effective buffer size, the safe time estimation and buffer size adjustment are carried out based on activities' precedence relationships. Firstly, the safe time in the activity is extracted based on the three-point estimation method in PERT; according to the characteristics of different precedence relations, the safe time is extracted from the time interval between activities. Secondly, the buffer is adjusted by the improved resource tension, the complexity of lap network and the connection degree of adjacent activities. Finally, Matlab software is used for case simulation, and the proposed method is compared with the classical method. The results show that compared with the root-variance method, the proposed method can shorten the project duration by 9.01% and reduce the cost by 5.18%.