Abstract: The few group cross section calculation model generates node homogeneous few group cross section for core 3D diffusion calculation, which is one of the key models of core calculation code. CYCAS is the new core 3D nuclear design code developed by Shanghai Nuclear Engineering Research & Design Institute (SNERDI). A new model based on detail analysis of the factors affecting node cross section was developed for CYCAS. In the model, the energy spectrum correction method was used to process the second order effect introduced by energy spectrum change, and the micro-depletion correction method was utilized to treat depletion history effect. The numerical results of unit assembly and AP1000 core validate the high accuracy of the new model within CYCAS.