Abstract: The resistance characteristics for the assemblies affect the flow flux distribution for the different types of assemblies in the core, which has a crucial effect on the design of the core. In order to improve the calculation accuracy and efficiency of the flow resistance characteristics for the core fuel assemblies, two types of assemblies among the six types fuel assemblies in the fuel zone were conducted by modular and integral threedimensional numerical simulation in this paper, so as to obtain the flow resistance characteristics of these two types of assemblies. The simulated results were compared with the experimental results of the full assemblies under the same conditions. The results show that the calculation time required for the modular simulation is about 1/6 of the integral simulation when predicting the flow resistance characteristics of all fuel assemblies in the core, but the pressure drop of the integral threedimensional numerical simulation is more consistent with the experimental results, and has the smaller simulated error. Finally, the effect of velocity and temperature to resistance characteristics was deeply studied to provide technical support for the scheme selection for studying the flow resistance characteristics of various assemblies in the core.