Abstract: A three-dimensional semicircular cold model of COREX melter gasifier was established for physical simulation. The particle motion information in the raceway was obtained by using high-speed photography to track the particle motion. The particle velocity scalar field was obtained through processing the data of particle motion information. The irregular degree of raceway boundary determined by the iso-velocity contour was discussed. The boundary of raceway is thereby determined precisely. The results can provide precise boundary conditions for macro kinetic calculation of raceway and numerical simulation.