Abstract: Based on the Navier-Stokes equation and renormalization group(RNG)κ-ε turbulence model,the flows around the nuclear fuel stick and the weld cavity were simulated numerically by the SIMPLEC algorithm.The body-fitted coordinates,staggered grid method and self-adaptive technique was utilized in this study.Through the analysis of flow around the nuclear fuel stick and the weld cavity,the defect of the old structure was found out,and two methods to improve the welding efficiency were proposed.