The development of metal 3-D printing technology was summarized in this paper. The advantages and disadvantages of various types of 3-D printing technologies were illustrated, main technical features of several typical 3-D printing technologies were discussed though their development history and working principles. On this basis, the future research direction of selective laser melting was put forward: The selective laser melting has a wider range of applications. The metal 3-D printing technology could be improved by promoting material performance, equipment function, structure design, and manufacturing technology. With the development of metal 3-D printing technology, the technologies will be more widely available in metalworking industries, and become the one of most important technology and strategic manufacturing technology.