Abstract: To investigate the influence of layer thickness on the microstructure and mechanical properties of laser powder bed fusion processed GH3625, specimens were prepared with different layer thickness while other parameters remained unchanged before they were studied in aspect of microstructure and tensile properties. It is shown that the density of specimens has not been influenced by layer thickness under a wide range of processing parameters. Besides, with optimized processing parameters, specimens with a density over 99.9% can be fabricated by 0.02 mm and 0.03 mm layer thickness at the same time. The increase of the layer thickness will lead to the change of molten pool morphology, and also significantly change the grain morphology. When the thickness of powder bed was 0.02 mm, the average grain size was about 18.128 μm, and the grain had obvious preferential orientation. At this time, the adjacent molten pools differ greatly in shape, showed the phenomenon that one secondary was deeper and wider, and the other secondary was shallow and narrow. When the layer thickness increased to 0.03 mm, the temperature gradient difference decreased, the morphology difference of adjacent molten pools was small, the elongated grains in the microstructure decreased, the average grain size decreased to 11.921 μm, and the preferred orientation of grains also weakened. Due to changes in grain structure and grain size, the yield strength was increased by about 5% in the 0.03 mm specimen than that of the 0.02 mm specimen in vertical direction, contributing to less anisotropy in mechanical property.