Project Mangement have been noteworthy ,and authors said different mannar for project scheduling. Some of the industrial countries utilize critical chain that recommended from Dr.Eli.Goldratt on the basis of theory of constraints for planning scheduling projects..Dr.Eli.Goldratt presented a mannar on the basis of Goals and schemes of the work of the factories that is named theory of constraints philosophy.Theory of Constraints was on the basis of the continuous improvement and the centralization was on the identifying constraints. On the purpose of increase the products of the factory. Dr.Eli.Goldratt demonstrates the application of his theory of constraints to project management in critical chain novel. In critical chain method with the use of relationship between tasks, required resources and access of the resources, the duration of the project network identified,and for the remedy of the critical tasks delay, discretionary duration correlated to the critical tasks,transferred to the end of the project.this time is named Project Buffer. Also Feeding Buffers are added to all paths feeding in to the critical chain to prevent the delays on those paths from effecting the on-time start of critical tasks. In this Research , we introduce 4 methods for determining feeding project buffer sizes with the use of 3 times pert estimated in critical chain project scheduling such that the duration of each tasks followed lognormal distribution . the with the simulation the offered method compared with the Critical Path,,cut paste, Root Square Error Adaptive Procedure methods. At The End 6 problemes analyzed with these methods and findings are demonstrated. Key Words Project Schedulling,Critical Chain,Project Buffer,Feeding Buffer, Buffer Sizing Methods,Pert Network
