Background： The plight of a large number of spent fuel accumulation can be effectively alleviated by constructing spent fuel dry storage facilities. Having been widely adopted in foreign countries, spent fuel dry storage technology has not yet been studied in our country. Purpose： The aim is to study the criticality safety of spent fuel dry storage facility. Methods： The research object is HI-STORM 100 spent fuel dry storage facility internal loading AFA-3G fuel assembly in this paper. Using the MCNP （Monte Carlo N Particle Transport Code） 4C code, criticality safety was studied by changing the density of the water inside and outside of the storage facilities. Results： The results indicate that kerr is far below 0.93 in the normal condition, which is safety. But there would be some problems if the water density is greater than 0.8 g·cm^-3 under accident condition. Nuclides composition based on burnup credit can be got by using ORIGEN-ARP code. And then calculation study on the critical safety of dry storage facilities in the same model was carried out. Conclusion： It is possible to provide some proposals on the research of criticality safety.