Abstract: Inserting feeding buffer in non-critical chain may lead to new problems, such as new resource conflict, non-critical chain overflow, etc. These problems further complicate the resource constrained project scheduling. In order to optimize the sizing of feeding buffer, based on root square error method （RSEM）, independent float is applied to solve the feeding buffer setting in critical chain project management theory. Using independent float wish is the hidden safety time in project network, the activities on non-critical chain are differentiated. Aiming at the non-critical activities which have independent float, and changing the latest time execution strategy proposed by Goldratt, the new feeding buffer sizing approach is built. At the end, experimentation of different plans using various feeding buffer sizing methods has been done by means of simulation for contrastive analysis. Results show that the new approach reduces the problems caused by the feeding buffer inserting and improves the due date and execution performance of project.