The particle velocity contours were obtained by tracking the tracer particles in the raceway region of the COREX melter gasifier model and the contours were irregular.According to the fractal theory,the fractal dimensions of different particle velocity contours were determined.Through the analysis of the fractal dimensions,a new method for precise determination of the raceway boundary was proposed.The results show that,when the velocity is less than 0.18m/s,the particles are located in the stagnant zone and the fractal dimensions of particle velocity contours are almost constant as 1.41;when the velocity increases from 0.18 to 0.83m/s,the particles are located in the rapid movement zone and the fractal dimensions decrease gradually from 1.41 to 1.05;when the velocity is greater than 0.83m/s,the particles are located in the cavity zone and the fractal dimensions are again almost constant as approaching to 1.00.Therefore,the velocity contour of 0.18m/s,which is critical to distinguish the rapid movement zone and stagnant zone,can be used to define the raceway boundary.Based on this method,the effect of blowing rate on raceway size was calculated and the results show that the penetration depth and height of the raceway increase with the increase of blowing rate. The particle velocity contours were obtained by tracking the tracer particles in the raceway region of the COREX melter gasifier model and the contours were irregular. According to the fractal theory, the fractal dimensions of different particle velocity contours were determined. Through the analysis of the fractal dimensions, a new method for precise determination of the raceway boundary was proposed.The results show that, when the velocity is less than 0.18 m / s, the particles are located in the stagnant zone and the fractal dimensions of particle velocity contours are almost constant when the velocity increases from 0.18 to 0.83 m / s, the particles are located in the rapid movement zone and the fractal dimensions decrease gradually from 1.41 to 1.05; when the velocity is greater than 0.83 m / s, the particles are located in the cavity zone and the fractal dimensions are again almost constant as approaching to 1.00. Herefore, the velocity contour of 0.18 m / s, which is critical to distinguish th e rapid movement zone and stagnant zone, can be used to define the raceway boundary. B. based on this method, the effect of blowing rate on raceway size was calculated and the results show that the penetration depth and height of the raceway increase with the increase of blowing rate.