Due to the rapid melting and solidification leads to complex transient temperature distribution during the selective laser melting (SLM) forming process, the molten pool and the cooling rate affect the final solidified structure, which affects the quality of the part. In this paper, a three-dimensional transient finite element model is established to numerically simulate the forming process of a single-channl multilayer SLM of GH4169 alloy to study the transient temperature distribution, molten pool size and cooling rate; and the influence of different linear energy density on the single-channl multi-layer SLM forming. The results show that when the linear energy density is 170 J/m, with the increase of the number of layers, the maximum temperature of the molten pool, the size of the molten pool and the heat-affected zone gradually become larger, and the upper layer has a remelting effect on the lower layer; except for the first layer, the cooling rate increases slightly with the increase of the number of layers. With the increase of the linear energy density, the maximum temperature of the molten pool at the center point of the fifth layer increases, and the the size of the molten pool and the heat-affected zone become large, the cooling rate increases with the increase of the linear energy density. Forming thin-walled wall samples with different linear energy densities, then comparing and analyzing the simulation results, a better consistency is obtained.