The invention provides a silicon nitride preparation method. The preparation method comprises the following steps: preheating a raw material silicon halide and/or silicon hydrohalide and/or silane tofirst temperature to form first reaction fluid; preheating a raw material nitrogen and/or ammonia gas to second temperature to form second reaction fluid; inputting the first reaction fluid with firstflow velocity and the second reaction fluid with second flow velocity in a fluidization reaction apparatus, adjusting the first flow velocity and the second flow velocity so that mixed fluid in the fluidization reaction apparatus can reach third temperature, reacting the silicon halide and/or silicon hydrohalide and/or silane, and nitrogen and/or ammonia gas at the third temperature to obtain silicon nitride, wherein the first temperature is less than the third temperature, and the third temperature is less than the second temperature. The reaction temperature can be regulated and controlledin a flexible mode, the temperature of the mixed fluid is controlled in a strict specific temperature range, the silicon nitride type corresponding to the specific temperature range is generated, mixing of out-phase silicon nitride cannot be generated, purity is high, instant reaction is carried out, and production speed is fast.