Abstract: The Monte Carlo transport code TOPAN was developed and it can be used to simulate the problem of the neutron and photon transport. The parameters of the point flux, surface flux, cell flux, surface current can be given by TOPAN. Besides the familiar capabilities of the conventional Monte Carlo code, TOPAN has the equivalent mass thermal motion model used for the neutron transport in the water at different temperatures, the transport module in nonuniform material, and the function of particle flag. These make TOPAN to be capable of simulating the neutron and photon transport for some complicated problems. The example was given to validate the modules of TOPAN.