In order to address project delays caused by uncertain factors in the construction project schedule management process, a new method for calculating the size of critical chain buffers is proposed. Taking into account process uncertainty and based on the GERT network, the correction process and duration of different logical processes are provided to transform the uncertain network into a deterministic one. By combining the critical chain management method and information entropy theory to assess the impact of increasing uncertainty in the merging process on the critical chain buffer, a calculation model for the critical chain buffer size based on the GERT network is established and analyzed using a numerical example. The feasibility and effectiveness of the model are verified through an example, demonstrating its ability to reduce project risks and shorten the construction period while ensuring a high probability of project completion.