The surface roughness calculation model based on powder properties is established by using the least square mean line method. Selective laser is used to melt molded Ti6Al4V single track and parts. The surface roughness of molded parts is detected by surface profiler and the geometric size of molded single track is observed and measured with optical microscope. The cause of errors between the theoretical and experimental value of the built model is analyzed. The experimental results show that the laser remelting zone has a great impact on the precision of the surface roughness calculation model. The average relative error between the theoretical and experimental value is 5.7%. The error is small, and the model has a practical engineering application value. The molded parts are mainly composed of α and β phases, and the micro-hardness is 487.3 HV0.3.