Abstract: The influence of configuration designs and magnetic field on n/γ discrimination for the slot-calibrated PIN fission chamber detector system was calculated by using MCNP code.Based on the 2 MeV neutron sensitivities,the n/γ discriminations of the system were obtained.The results indicate that the design of the system can meet the needs of practical measurements with n/γ discrimination greater than 5 without a magnetic field.And with a magnetic field,the n/γ discrimination can be increased more than 100 times.