Abstract: For the HTR core physical calculation,the modeling of strong absorber region in diffusion theory is a well-known problem,even with the homogenization treatment.The problem is how to take the advantage of high performance computing for solving diffusion equation,and at the same time to keep accuracy as transport theory.The method of equivalent cross section is proposed based on the combined transport and diffusion theory.The homogenization method is used to estimate the homogeneous cross section by volume-weighted in the control rod region.The modified diffusion constant of the control rod region is derived from the fact that the net current at the interface of the control rod region calculated by diffusion theory must be equal to that by transport theory.These equivalent cross sections can be directly used in the diffusion equation and there is no need to adjust the diffusion solver.The method of the equivalent cross section has been used to the region of the 2-dimensional transport calculation.And improvement is proposed to divide the mesh of the absorber region in the process of the calculation of the equivalent cross section.It is verified in different mesh configurations.The numerical result demonstrated the good performance and improvement of this method.