Abstract: The thermal hydraulic experiment of 5×5 helical cruciform fuel (HCF) assembly was conducted in this paper, the resistance and mixing coefficients of HCF assembly were obtained. The frictional pressure drop of the test section was measured, and the resistance coefficient correlation of HCF assembly was fitted. The mixing characteristic of the test section was analyzed with energy balance approach. The cold fluid was directly injected into one of the sub-channels, the T-type thermocouple was fixed into the central of subchannel, and the fluid temperature of the sub-channel was measured. The transverse mixing of HCF assembly was comprised with turbulence mixing and lateral flow diversion, and the effective mixing coefficient was defined to describe the transverse mixing. The effective mixing coefficient of HCF assembly does not change distinctly with Reynolds number, and the mean effective mixing coefficient is 0.019. The effective mixing coefficient was input to the sub-channel analysis code Cobra-tf, the temperature distribution of the sub-channel was calculated. The calculated temperature correspondes well with experimental data, the average deviation is 0.16 ℃.