[en] The shielding design calculation of high energy accelerator facility is usually performed by using the Moyer model based on single neutron energy-group approximation, since in the GeV region the neutron attenuation length is nearly constant independently to the energy. While in the medium-energy region below 1 GeV the neutron attenuation length increases largely with the energy. In this work, we tried to develop an analytical method for calculation of dose equivalent H(E_n) through bulk shield in the 50-250 MeV accelerators, which corresponds to a modified Moyer model based on multi-group approximation in the following procedure; H(E_n) Ho.k.exp(-ρ/λ(E_n).t)/r². (1) Systematic calculation of the neutron attenuation lengths λ(En) in thick (2 m) concrete shield by using one dimensional discrete ordinate transport code ANISN-W together with the cross section data library DLC119 (HILO86). (2) Evaluation of accuracy to estimate the dose equivalent of neutrons obliquely incident to thick concrete shield using the above attenuation lengths. This evaluation has been done with the three dimensional Monte Carlo code MCNP- 4B. (3) Estimation of neutron build-up effect k due to the neutron scattering inside the room and near the concrete surface. This new model is expected to have higher accuracy than other existing analytical models, and we plan to investigate the applicability of this method by comparing with the accurate Monte Carlo calculation results and the experimental results. (author)