Selective laser sintering (SLS) technology is developing rapidly and has been highly technology maturation, which can build complex insulation structures. However, it is difficult for traditional injection molding process to make some insulating parts with complex structures. Therefore, SLS technology has significant advantages in the production of complex insulating structures. However, different process parameters have great influence on the properties of samples. The density and insulation properties of nylon 12 samples under different laser powers were studied. Different laser powers were selected and the density, breakdown strength, conductivity and permittivity were taken as experimental indexes to select the optimal laser power. The mechanism of thermal oxidation degradation of nylon 12 was analyzed which resulted in the properties deterioration of samples. The results show that the density and insulation properties of samples are improved, then stabilized and degraded in the range of laser power. The optimal laser power is 9 W, the scanning speed is 3000 mm/s and the scanning spacing is 0.1 mm. The density of samples is 1.0106 g/cm³, the DC breakdown strength is 81.57 kV/mm and the conductivity is 4×10^-13 S/cm.