Abstract: In order to reasonably quantify the uncertainty in calculated k_eff due to uncertainties of nuclear data, the SURE code used for sensitivity and uncertainty (S/U) analysis of integral parameter k_eff was developed. The method of multi-group discrete ordinates (S_N) was used to calculate k_eff, flux and adjoint flux for applications. Perturbation theory was used to determine the sensitivity of the calculated value of k_eff to the nuclear data used in the calculation. The uncertainty in the calculated value of k_eff, resulting from uncertainties in the basic nuclear data used in the calculation, was estimated using energy-dependent relative covariance matrices. The multi-group cross sections for S_N transport calculation, the reaction channel multi-group cross sections and the neutron transfer matrices for sensitivity calculation, multi-group covariance data were processed from ENDF/B-Ⅶ.1 nuclear data library. The sensitivities of calculated k_eff on Godiva and Jezebel benchmarks to nuclear data and the contribution of the cross section uncertainties to the uncertainties of k_eff were analyzed using SURE. The calculated sensitivities of SURE are in good agreement with those of MCNP and FORSS codes.