In order to reduce cracks in cladding layers caused by large temperature gradient in laser cladding technology, preheated matrix in laser cladding process was used to reduce temperature gradient. The finite element model of multi-lap temperature field of laser cladding nickel-based metal powder on 45# steel substrate was established by using ANSYS software. The reliability of the model was verified by thermocouple temperature measurement. Temperature gradient of cladding layer on the edge of cladding layer during the cladding process and the effect of the preheating temperature of the substrate on temperature gradient of cladding layer were analyzed by the finite element model. The results show that the maximum temperature gradient is located at the edge of the bonding interface between the cladding layer and the substrate. It is an extreme condition for the solidification of the metal molten pool and causes the crack to be easily produced here. With preheating temperature of 200℃, the substrate preheating can significantly reduce the temperature gradient during the solidification process of the cladding layer, and the decrease of the temperature gradient is more obvious, which can effectively inhibit the crack generation. The combination of simulation and experiment provides a practical reference for the actual laser cladding manufacturing.