Abstract: The simulation calculation of neutron importance on fast neutron burst reactor （CFBR-II reactor） is introduced in this paper. The three-dimension model with complicated structure of CFBR-Ⅱ reactor is finished using MCNP program and the calculation of neutron value is realized by neutron multiplication method. In order to eliminate the difference of using the relative neutron importance in the hole of steel salver instead of the one in the core and reflector, the uniform sampling technique is applied to study the neutron importance detailed distribution along radial. The results indicate that the maximum neutron importance lies in areas of enrichment uranium or middle certain layer but not in system center or sphere core, the other areas are monotone descending along radial.