Abstract: To delve into the impact of nuclear data uncertainty on the effective multiplication factor calculation for the JRR-3M research reactor, this study established a nuclear data uncertainty quantification process based on SANDY. The specific methodology involved perturbing important reaction pathways of the target nuclides with SANDY to generate perturbation files, processing these files with NJOY, and ultimately utilizing OpenMC for Monte Carlo simulations. The influence on the effective multiplication factor due to several key nuclides (such as ²³⁵U, ²³⁸U, Hf, etc.) data uncertainty was calculated and analysed for three operational conditions of the JRR-3M research reactor. For critical, control rods fully inserted and control rods fully withdrawn conditions, total effective multiplication factor uncertainties are 660.8×10⁻⁵, 588.5×10⁻⁵ and 708.4×10⁻⁵, respectively. In all operational conditions, the impact of the fission release neutron energy distribution of ²³⁵U is the most notable. The study reveals that within hafnium control rods only the nuclear data uncertainty of ¹⁷⁷Hf plays a major role.