The present invention provides a SHS process for preparing high alpha-phase Si3N4 powder and Si3N4 whiskers. For preparation of high alpha-phase powder the additive alpha-Si3N4 content is 10-100 wt% of silicon powder, NH4F+NH4Cl+CaF2 content is 1-60 wt% of silicon powder content, the nitrogen gas pressure for retaining SHS reaction is 1-30 MPa, the specific surface area of the obtained ultrafine Si3N4 powder body is in the range of 2-6 sq.m/g, and its equivalent grain size of adjustable in the range of 0.3-0.9 micrometer. For preparation of Si3N4 whiskers beta-Si3N4 whisker reactant component is Si powder, beta-Si3N4 powder is 5-15 wt% of silicon powder content, NH4Cl is 1-60 wt% of silicon powder content and analytically pure Al powder is 0.5-5 wt% of silicon powder content. |