Using simulation to guide the process optimization of large and complex structural parts can save a lot of manpower and material resources. Based on the simulation method, the effect of pouring process including pouring time and temperature on the secondary dendrite arm spacing microstructure of gravity cast aluminum silicon alloy body was studied. The results indicate that there is a good correspondence between the simulation and experimental results for the material level step sample and the gravity cast aluminum silicon alloy body, and the deviation of simulation is relatively small. The secondary dendrite arm spacing first decreases and then increases as the pouring temperature increases when the pouring time is constant or as the pouring time increases when the pouring temperature is constant, and the optimal pouring temperature and time are 695 ℃ and 60 s respectively. In addition, the solidification time first decreases and then increases with the increase of pouring temperature when the pouring time is constant or with the increase of pouring time when the pouring temperature is constant.