Abstract: An accurate physics calculation model has been set up for the mini-type sodium-cooled fast the basic physics characteristics of MFR can satisfy the requirement and objectives of the core design.The power density and neutron flux distribution are symmetrical and reasonable.The control system is able to make a reliable reactivity balance efficiently and meets the request for long-playing operation.reactor（MFR） based on MCNP-4C code,then a detailed calculation of its critical physics characteristics,neutron flux distribution,power distribution and reactivity control has been carried out.The results indicate that