Abstract: Integral experiment is one of the important means to check nuclear data, and accurate simulation calculation is an important step in the research of integral experiment. When the MCNP-4C program is used for simulation calculation, the source neutron characteristic parameters, including the source neutron energy spectrum angle distribution and pulse time distribution, are the key contents of the simulation input file, and directly affect the accuracy of the simulation results. The polyethylene sample is often used as the standard sample to verify the integration experiment system, so it is used to study the influence of the characteristic parameters of the source neutron on the simulation results. In order to study the influence of subtle changes of neutron parameters on the leakage neutron spectrum of polyethylene samples, the angle distribution of neutron energy spectrum was changed by changing the ratio of D-D neutron yield to D-T neutron yield, and the pulse time distribution was changed by adjusting the pulse time distribution half-width. The leakage neutron spectra of 47°, 61°and 79° of polyethylene sample were simulated with slight changes in the angular and pulse time distributions of source neutrons respectively. The results show that the angular distribution of the source neutron energy spectrum mainly affects the low energy region of the leakage neutron energy spectrum. The change of pulse time distribution mainly affects the high-energy region of the leakage neutron energy spectrum. In order to accurately describe the source neutron, obtain accurate energy spectrum angular distribution and pulse time distribution of the source neutron, and obtain more accurate simulation data, the monitoring system of the integral experiment was upgraded. A SiC detector with higher energy resolution was used to measure the associated particles to obtain the D-D neutron yield and D-T neutron yield indirectly. A small size liquid scintillator detector with better neutron gamma discriminating ability was used to monitor the pulse time distribution of source neutrons. After processing the measured results of the upgraded monitoring system, the source neutron characteristic parameters were obtained and described in the MCNP-4C program. The 47°, 61° and 79° leakage neutron spectra of polyethylene samples were simulated using CENDL-3.2, ENDF/B-Ⅷ, JENDL-5 and JEFF-3.3 databases, respectively. The simulation results were compared with the measured results under the same experimental conditions. The results show that the simulation results are in good agreement with the experimental results in the n-p scattering energy region of the three angles, which lays a foundation for further improving the accuracy of the integral experimental simulation data.