Abstract: In order to decrease the fluctuation of electrons record at imaging plane in MCNPs simulation of X-ray radiography, a new method was tried for creating virtual X-ray source with pointing probability method. The virtual X-ray source may generate the next main electrons which has contribution to the detector. This method can not only increase the possibility of the electron, but also make a history contribute pixels as much as possible. The comparision of the results whether using the proposed method or not was carried out. The results show that the using of the method could decrease the fluctuation of the electrons contribution effectively, improve the presion of the result, and develop the simulation capability of MCNP for X-ray radiography.