The morphology of the sample’s upper surface is primarily related to the melting width, and there is slight powder sticking, spheroidization, and splashing in some areas; the morphology of the up-skin and vertical surfaces is greatly affected by the powder sticking and spheroidization, which is related to the width of the melt channel, Furthermore, the hatch distance, powder diameter, and forming angle are directly related. The powder adheres more on the up-skin surface than the vertical surface regardless of the process parameters, and most of the powder does not melt, which decreases the surface quality of the oblique side. The liquid phase area of the molten pool increases with the increase in the line energy density. Hence, the melt width is directly proportional to the laser power and line energy density and inversely proportional to the scanning speed. The larger the melt width, the smaller the upper surface roughness; as the line energy density increases, the energy accumulation effect increases the surface temperature of the molded part. Moreover, the temperature rise on the up-skin and vertical surfaces cause the powder spheroidization and sticking phenomenon in the contact area and the powder pile substantially grows in size, thereby increasing the surface roughness value of the SLM molded part. The predicted value of theoretical roughness and the actual measured value are basically the same under different process parameters. Additionally, the prediction error of the upper, vertical, and up-skin surfaces are less than 20%, 30%, and 15%, respectively, which can be used to predict the surface roughness of 316L stainless steel SLM molded metal powder parts under different process parameters.