Based on AMS270E "high temperature measurement" , a test program for the uniformity of moving slab in a large continuous heat treatment furnace is designed by using the self-developed black box furnace temperature measurement system, the uniformity of S35c slab continuous heat treatment furnace in a steel plant was tested and analyzed based on the design. The test results show that the self-developed black box furnace temperature test system can meet the temperature uniformity test requirements of continuous motion of high-temperature Slab. The temperature of the slab increases rapidly after being fired, and gradually reaches the target temperature and enters the homogenization stage. Compared with the data of the homogenization stage, the temperature at each position of the slab reaches the target, and the overall temperature uniformity is good, the heat treatment temperature and time of slab in furnace are consistent with the requirement of process design. It provides an effective method for homogeneity and slab test of large-scale continuous furnace.