Abstract: In order to realize fast calculation for the reactor facility shielding problem, it is necessary to establish a spatial discrete scheme for SN equation that can reduce the negative numerical flux, ensure the linearity of the iterative scheme, and achieve good accuracy in a large grid with minor calculation effort. This study is based on the spatial analytic solution of the within-group fixed source SN transport equation, and uses the analytic basis function method to expand the spatial term. In order to improve the calculation efficiency, the weighted coefficient method is used to avoid a large number of exponential operations in a single grid. High order source expansion is studied to improve the precision. Finally, a fast iterative scheme for the self-scattering source iteration is realized based on the Krylov subspace method. The numerical results show that this method can obtain great advantages in the optical thick medium with uniform material area, and can be used for the rapid calculation of shielding problem of large reactor building.