Most resources used in a project will have an easily determined cost. We need to know which staff members can work on which parts of a project and what needs to be done, and when. Project time management should be broken down, step by step, just as other parts of the project are broken down in the planning phase. This will help make sure that everything is done when it needs to be, and to keep the project from going over its budget because it went well past the time scheduled for it. A project manager often need to control the whole time of the project and grasp the key process in those tasks which can shorten the period and reduce the cost. This paper discusses the algorithm of AOE-net in the critical path and its application to evaluate the completion time in the network planning of project time management.