Abstract: It is well known that the computation time of multigroup Monte Carlo calculation is much less than that of the continuous (point-wise) calculation. However, there are some difficulties in the multigroup treatment about resonance and self-shielding. Although the good precision of point-wise cross section transport calculation can be obtained, the consumed time is too long. A coupled calculation of the multigroup and the point-wise cross section was developed in self-development 3D neutron and photon transport Monte Carlo code MCMG. The validity of this method was proved by testing of many models. The almost same results with the point-wise cross section MCNP code were achieved. The coupled calculation of MCMG is about one time faster than that of MCNP.