Abstract: At present, there are two ways of post-welding heat treatment and rough grinding position arrangement in the domestic welding rail base: one is heat treatment first, and the other is coarse grinding first. The 1mm thickness welding slag of the joint before and after rough grinding can protect the joint and prevent the harmful tissues such as martensite from being generated due to the excessive cooling rate in the process of blast cooling in low temperature environment. In order to explore the air-jet cooling process of joints with welding slag, this paper establishes a jet cooling model based on the coupling system of the FLUENT module and the transient thermal module under the ANSYS platform. The simulation results show that the flow velocity in the region with larger rail surface curvature is larger, and the flow velocity in the region with smaller rail surface curvature is smaller. The cooling speed at different positions of the joint is sorted from slow to fast as follows: the center of the rail head＜the triangle of the rail bottom＜the waist of the rail bottom＜the foot of the rail bottom. After the end of cooling, the highest temperature of the joint appears in the center of the rail head, and the lowest temperature appears in the foot of the rail. Joints with welding slag have a higher temperature than those of polished joints during the cooling process of air spray, and the cooling speed is smaller.