Abstract: This paper explored the forming quality of S136 alloy in different contour sizes by selective laser melting. With the same forming parameters, plane scanning and strip scanning strategy were used to form specimens with different contour size. Through the comparison of porosity, density and hardness of different specimens, the study explored the selection of scanning strategy under different contour size. The results show that when the contour size is less than 15 mm×15 mm, the plane scanning strategy will get better forming quality, and it will be easier to plan the scan path. But if the contour size is greater than 15 mm×15 mm, the preheating effect between long scan channels will decreases, so the strip scanning strategy will have better effect. In practice, the scanning strategy should be selected according to the contour size to obtain better process quality.