Abstract: Simulation of the aerodynamic effect of Apollo reentry capsule under high enthalpy flow and the numerical factors influencing the predicted heat flow were studied. Employing ESI-CFD-FASTRAN software as the numerical simulation platform, the heat flux model based on temperature gradient and molecular diffusion effect was used. The spatial discretization used the Roe-FDS scheme, and the time marching used point implicit scheme. The numerical experiment shows that:(1) The heat flux reaches an extreme value at the stagnant of the mode, and the heat flow along the wall decreases continuously; (2) Grids satisfying the grid-Reynolds-number obtain accurate heat flux; (3) Gupta model calculated the heat flow is higher than that of the Park85 model, but the distribution is similar. (4) The turbulence model was used which obtain the same results as the laminar flow. (5) The second-order minmod limiter makes the heat flux on the shoulder relatively higher, but the overall heat flux distribution is lower than that of the non-limiter. Therefore, it is more accurate for predicting heat flux using mesh satisfying grid-Reynolds-number and using high-order-limiter; Gupta mode will obtain higher magnitude comparing to Park85 mode that will ensure the security in engineer application; Laminar mode results is the same as turbulence.