Abstract: The neutron detector response function is the effective connection between the numerical simulation results and the detector readings, which shows the contribution for the detector readings from rounding areas. In this paper, the formula of the response function was given and calculated using MCNP code. The interfering factors to the response function were analyzed. The analysis results show that the factors that have great influence on the neutron absorption characteristics, such as boric acid, control rod and burnable poison, have significant effect on the response function of the neutron detector. Other effects not referred in this paper could be analyzed by the same method.