Abstract: A small-sized modular sodium cooled fast reactor called M1 was designed by China Institute of Atomic Energy (CIAE). As an encapsulated nuclear source with thermal power of 3 MW, M1 system adopts modularization, by which the core will be loaded, then shipped and assembled onsite. Considering factory’s special conditions for loading and active chemical property of sodium, a special loading pattern, loading fuel first, then sodium filling, was adopted for M1. Through MCNP code simulation calculations, the results indicate that 5-batch loading scheme is reasonable according to the principles and nuclear measurement system of loading. Two miniature fission ionization chambers placed in the core also monitor k_eff of the core during the course of sodium filling. Finally a sound loading scheme of small-sized sodium cooled fast reactor in a factory is formed, which can provide inspiration and guidance regarding loading of other small reactors.