Abstract: The MONK code was used to analyze the nuclear critical safety of the fuel storage tank for the MOX hot room project. The fuel partition storage method was determined by the given tank size and fuel rod number. The critical benchmark data published internationally were selected to verify and determine the MONK code to calculate the bias and subcritical limits of similar material forms. The conservative hypothesis was carried out to determine the effective neutron multiplication factor of the storage tank which was under normal and accident conditions, and to evaluate the safety of the storage tank. The calculation results show that the maximum neutron multiplication factor of the storage tank is less than the sub-critical limit under the most dangerous accident condition, and the system is in the critical state of safety.