Aiming at the problems of high surface roughness, poor forming quality, and post-processing such as machining after printing of laser deposition manufacturing (LDM) formed parts, the forming platform is built independently to print thin-walled parts with different inclination angles by using the process method of “small spot, small layer thickness and small powder particle size”. Based on the principle of layered slicing of additive manufacturing, the theoretical surface roughness prediction model of typical thin-walled parts under different geometric characteristics is given. On this basis, the control strategy of surface roughness of laser deposition manufacturing parts is proposed. The results show that it is feasible to obtain the prediction model of the mathematical model by rotating and translating the surface roughness prediction model of the component by combining the fusion lap with the step effect. The main parameters of the roughness prediction model are the fusion lap offset, the interlayer lift and the tilt angle. When the fusion lap offset is 0.5 mm, the upper surface roughness of the part is 10.5 μm. When the interlayer lifting amount is 0.15 mm, the surface roughness of the vertical side is 12.214 μm, and the theoretical error of the surface roughness of the inclined side with the forming angle of 60° is the largest. The powder adhesion phenomenon is the main reason for the large error.