Abstract: For the purpose of analyzing the impact of PyC layers, internal pressure etc. on the thermomechanical performance of TRISO coated fuel particle, a 3D thermo mechanical coupling model was developed for TRISO coated fuel particle with UN as the kernel by using the multi-physics coupling software COMSOL, and the model was validated against the IAEA CRP-6 benchmark. Performance analysis of the TRISO coated fuel particle with typical design parameters was conducted under steady state and reactivity introduced accident (RIA) conditions. The results show that the SiC layer maintains its structure integrity, but the IPyC layer has the potential of failure in steady state condition. Further improvement to the design of TRISO coated fuel particle is required. For the RIA condition, thermal expansion is a dominant factor resulting in the loss of structure integrity of the TRISO coated fuel particle. The model is capable of analyzing the performance of TRISO coated fuel particles with complicated multi-physics characteristics under the operation conditions of LWR, which is useful for further optimizing the FCM fuel design.