Flowing and mixing granular materials of two different sizes and densities in an industrial-scale screw conveyor was studied by computer simulation using the discrete element method(DEM). Quantitative analysis results by the Lacey mixing index showed that mixing performance of the screw conveyor was dependent strongly on operational conditions and structural dimensions. Both screw rotating speed and material feeding rate had dominant effects on mixing efficiency

followed by granular material sizes and screw pitch in the mixing region. To reduce energy consumption and improve mixing performance in production

reasonable operation parameters of screw conveyors could be selected according to these findings.