Abstract: Gas target is a significant technology roadmap to improve intensity of the fusion neutron. Due to the thermal effect of the beam and the circulating flow of the gas, the gas in target chamber is in a dynamic equilibrium state under operating conditions, which will affect the range of D⁺ ions in the gas target and the spatial distribution of neutron source intensity. It is essential to find a more accurate simulation method. In this paper, based on Monte Carlo particle transport coupled with hydrodynamic calculations, combined with the reaction cross section data, a simulation calculation method for the source intensity and spatial distribution of the gas target fusion neutron source was established. Using the existing experimental data to verify the calculation method, it is found that the relative deviation between the total source intensity calculation result of the new method and the experimental measurement data is only 5.9%, and the neutron source intensity distribution agrees well with the experimental detection data. On this basis, with reference to the design scheme of the windowless gaseous target and accelerator operating parameters of the intensive fusion neutron source scientific device (HINEG) under development, the gaseous target source intensity was simulated, and the neutron source intensities under different beam energy were calculated. The highest source strength index can reach 3.60×10¹³ s^-1.