The 3D gas flow field, including the gas pressure and gas velocity was studied by computer fluid dynamics simulation (CFD). The tower continuous vacuum dryer’s structure was improved and the pumping gas sketch was also optimized. The model was resoled by standard turbulence model. The porous medium zone was adopted to the material zone. The Darcy law, Ergun equation and porous medium interface jump boundary condition was applied. The effect of the drying intensity, vacuum pumping pipes setting and vacuum degree of gas outlet was analyzed. The result shows that the pressure of gas outlet should be maintained lower at 8000 Pa, and the pressure of grain inlet and outlet should be maintained at 9000 Pa. The vacuum pumping pipes should be set at the bottom of last drying stage of the drying room in order to improve the gas flowing direction, and to improve vacuum performance. The pressure and velocity of gas along height of dryer is not the main effect factor of drying quality. On the top of each drying stage of the vacuum dryer, two horny pumping pipelines were set. It has good velocity uniformity, but more simple compared with three horny pumping pipelines.