Abstract: General perturbation theory（GPT） is applied to study the contribution of the nuclear data to the uncertainty of the macroscopic cross section（XS） of fuel assembly of AP1000. Through the comparison and analysis of the contribution of the different uncertainty sources, the correlation matrix of macroscopic XS has been gained. At the same time, the sensitivity analysis and stepwise comparison methods had been used to study the mechanism of the contribution of nuclear data to the uncertainty of macroscopic parameters of fuel assembly of AP1000 under different operation conditions. The final numerical results indicate that the uncertainty of macroscopic XS propagated from nuclear data is, to some extent, constant. To the point the major contributors to macroscopic XS uncertainties are ²³⁵U nubar, ²³⁸U capture, ²³⁸U inelastic scattering and H-1 inelastic scattering. Also the numerical results include that the uncertainty of k_inf and the macroscopic cross section increases with the temperature rises. The uncertainty of k_inf increases with the decreasing of the enrichment of fissile material and the existence of burnable poison. At the same time, the uncertainties of fast group cross section are much larger than the thermal cross section uncertainties. Specially, the ²³⁸U（n,γ） and ²³⁸U（n,n’） should be received significant attention and made further evaluation and improvement.