Abstract: In order to analyze the sensitivity of variety of single activity completion time to project-s duration, by probabilistic analysis principle and approach, the probability of terminative time-s change of activity under different conditions was confirmed, and the system of decision evaluation index was designed which contains the method of confirming correlative parameters in the system on the basis of total float theorem. The sensitivity of variety of critical activity-s completion time to project-s duration was analyzed with the analysis technique of single-factor sensitivity, and how to select critical activities which are the most sensitive to total time limit from all activities considered. Finally the process was validated and illuminated by illustrating. The system is helpful to supervise and control the sensitive activity to project duration, and contribute to project scheduling and planning, which establishs theoretic foundation for analyzing multi-factor uncertainty problem of project-s duration.