Abstract: The inferior surface forming quality is a pressing issue that needs to be addressed for the application and promotion of SLM technology. The uneven forming surface has adverse effects on the mechanical performance and corrosion resistance of parts fabricated by SLM. Samples with a 45° inclination containing both up-facing surface and down-facing surface, as well as 90° vertical samples with vertical surfaces were fabricated by SLM. Taking these typical surfaces with 3 different construction angles as the research object, the surface formation characteristics under different construction angles were studied and compared, then the causes of these characteristics were analyzed and discussed. The SEM images showed that the up-facing surface of the 45° inclined sample mainly exhibited characteristics of stairs and slight particles adhesion, while severe particles adhesion and aggregation phenomena occured on the down-facing surface. The formation quality of the 90° vertical surface was primarily affected by the particles adhesion. Combining observation of the three-dimensional surface topography with non-contact surface roughness measurement and comparison, the influence of 2 main process parameters, laser power and scanning speed, on the surface formation quality was explored. Ultimately, under their respective process parameter windows, the smoothest surfaces of 4.0 μm, 21.6 μm, and 7.8 μm were achieved, and the optimized parameter combinations resulted in a reduction in surface roughness of 44%, 47%, and 56%, respectively. Additionally, the transformation patterns of different surface characteristics on the target surfaces of the 3 different construction angles under varying process parameters were analyzed from perspectives such as laser energy input, powder particles, and molten pool thermal processes. This helped to explain the influence of process parameters and propose strategies for parameter combinations leading to better surface formation quality.