The substrate for rice seedling raising is crushed by crushed waste straw, which can effectively reduce the environmental pollution caused by incineration. However, due to the low drying efficiency and uneven drying in the drying process of the substrate, the local drying space is extracted, and the motion law of the air around the substrate is simulated by the CFD technology. The influence of the shape and placement of different air outlets on the velocity distribution of air is discussed. Through detailed comparison of the air velocity distribution maps of different air outlets, when the outlet size is 8×230 mm and perpendicular to the length of the substrate plate, the air velocity distribution around the substrate is the best, almost zero speed zone. The analysis proves that this technology can save research cost and improve drying quality of substrate.