In order to reduce the hydrolysis rate of Si powder and inhibit the swelling and cracking of cast samples, Si powder was treated at different temperatures for 5 h, and then slurries and SiC-Si3N4 materials were prepared. The effect of the preheating temperature on the composition of the Si powder, the hydrolysis rate as well as the nitridation of the SiC-Si3N4 materials was studied. The results show that with the increase of the pretreatment temperature of Si powder, the oxidation degree of Si powders increases, the viscosity of the slurry with PAAS dispersant decreases gradually, and the hydrolysis reaction of Si powder decreases gradually; the Si powder pretreated at 700 ℃ or lower has little effect on the nitriding process, while the Si powder pretreated at 800 ℃ has a great effect on the nitriding process, which is not conducive to the nitriding sintering of the samples. Therefore, the Si powder pretreated at 700 ℃ for 5 h has the best properties, which not only has lower hydrolysis rate and good slurry fluidity, but also has mild effect on the nitriding reaction.