Abstract: Calculations of the effective multiplication factor (k_eff) for the core of the China Initiative Accelerator Driven System (CiADS) have been conducted based on various evaluated nuclear data libraries (ENDLs), revealing significant differences in k_eff values calculated by different ENDLs. The primary isotopes responsible for these differences have been identified as ²³⁵U, ²³⁸U, ⁵⁶Fe, and ²⁰⁹Bi through the substitution method of isotope. Sensitivity analyses have been conducted to indicate the sensitivities of reactions for k_eff in the CiADS core, ISC of the average number of fission neutrons, fission reactions, and capture reactions are generally consistent across different ENDLs. At the same time, the reasons for the k_eff differences in the substitution method are explained by analyzing the cross-section discrepancies in various ENDLs. The uncertainties of different reactions from different nuclides in various ENDLs have been quantified for k_eff of the CiADS core, and the covariance of some nuclides with relatively small sensitivity differences has been analyzed. The result shows that the total uncertainties of ENDF/B-VII.1, ENDF/B-VIII.0, and JENDL-5 are 2.487%, 1.005%, and 0.684%, respectively. ²³⁵U, ²³⁸U, ⁵⁶Fe, and ²⁰⁹Bi are the nuclides contributing most to uncertainty, among them, the average fission neutron number, fission reaction, capture reaction of ²³⁵U and capture reaction of ²³⁸U contributing most to uncertainty. This work highlights the reactions and sensitive energy regions of key nuclides for special nuclear data library development of ADS, as well as nuclear data measurement, nuclear data adjustment and related activities.