Producing high α-Si3N4 powder in fluidized bed is an advanced method with low cost and high production. Traditional investigations on silicon powder nitridation isolated the phase transformation from nitridation process, which brings difficulties in predicting and controlling the produced α/β phase ratio. In this paper, the silicon nitridation process was related to the final α/β phase ratio, and multiple related parameters were discussed. Thermal gravimetric analysis (TGA) instrument was used to detect the detailed nitridation process. Silicon powder with different specific surface areas (i.e., diameters) was used at temperatures just below their melting point (1410oC). The non-sharp interface model was implemented to simulate the nitridation and predict the ratio of α/β-Si3N4. Some key factors on diffusion and reaction were analyzed. The α/β ratio get from simulations were highly consistent with X-ray diffraction (XRD) tests. Mechanisms of powder diameter and thermal diffusion on the production of α/β-S...