Abstract: COCO, the core nuclear design code, was developed by China General Nuclear Power Corporation. Before its industrial application, the COCO code should be verified and validated thoroughly. Each theoretical model implemented in COCO code was validated with various international benchmarks. With usage of the lattice calculation PINE code and the flux mapping MAPLE code, the core simulation results from COCO were compared with the operational data from Ling’ao, Ningde and Hongyanhe power plants of China General Nuclear Power Corporation. The results show that the COCO code has favorable calculation accuracy.