Abstract: This article starts from the theory of low-energy photon/electron transport and based on the low-energy photon/electron transport related data in the ENDF/B-VI.8 database, simulates the photoelectric effect process from a subshell perspective, and considers the physical process of atomic relaxation. At the same time, the sampling process of atomic relaxation subshell is added to further improve the Monte Carlo simulation process of low-energy photon transport. For low-energy electrons, a single event transport simulation method is adopted, which add four interaction processes: atomic excitation, elastic scattering, electroionization, and bremsstrahlung. The lower limit of the energy range for photon/electron coupling transport simulation in the NPTS program is extended from 1 keV to below 15 eV. By comparing the flux energy spectrum and spatial distribution spectrum of typical models with the JMCT program, the correctness of the NPTS program is evaluated based on 3σ conduct deviation testing based on principles. The test results indicate that the calculation results of the NPTS program are consistent with those of the JMCT program within the uncertainty range, verifying the correctness of the low-energy photon/electron coupling transport simulation function of the NPTS program.