Abstract: Effect of process parameters on size precision of melting copper powder forming parts by means of selective laser melting forming was studied based on orthogonal experiments. The influence of technological parameters on absolute error of forming dimension and the effect of various factors on dimensional accuracy were analyzed when the thickness of feeding powder was 0.05mm. The order of the influence of each process parameter on the absolute error of size is the scanning interval, scanning speed, laser power and scanning path. The optimum parameter combination is laser power of 360W, scanning speed of 1050mm/s, scanning interval of 0.08mm and scanning mode of spiral. The results show that, the absolute error of dimension increases with the increase of laser power and decreases with the increase of scanning speed and scanning interval. The influence of different scanning paths on the absolute error of size is small. The absolute error of size increases with the increase of bulk energy density within the range of factor. The research provides the basis for the selection of parameters in laser sintering of pure copper powder.