The selective laser sintering (SLS) is one of the important 3D printing technologies. In the sintering process of the polymer material the uneven shrinkage will cause warp and decrease the size of parts. The SLS processing parameters playing the major influence are discussed. Based on the theory of the gray relational analysis (GRA) in the SLS experiment with the polypropylene (PP) composite powder, the results show that the most important parameter is the scan speed. Considering the comprehensive effects of the warp and molding accuracy, the optimized fabrication parameters of the forming process are got as follows: the scanning speed is 1.9 m/s, the laser power is 16.5 W, the scanning width is 0.12 mm and the single layer of powder is 0.15 mm.