Abstract: Poor fusion is a common process defect in laser cladding. In order to explore the mechanism of poor fusion during inter-track overlap, single-track single-layer cladding test, multi-track single-layer cladding test, multi-track remelting test and single-layer tail-track remelting test were designed, and the simulation of temperature field during single-track cladding was carried out. The results show that the formation mechanism of the poor fusion defect is that the upper part on edge of the deposited area is raised, and the heat dissipation is slower and the melting is faster when the laser irradiates its surface. The laser energy input at the edge root is low and the shape is concave. so the heat dissipation is fast and the melting is slow. The molten liquid is turned out by the upper convex part and connected with the molten part of the root and the substrate, resulting in the gap between the root of the cladding layer and the laser, resulting in poor fusion defects. In order to reduce the occurrence of such poor fusion defects, a single-layer multi-pass lap test of the inclined cladding head was designed according to the mechanism of poor fusion. The results show that the inclined cladding head can effectively reduce the occurrence of poor fusion defects.