Numerical simulation was conducted to investigate the heat and mass transfer characteristics in a 12 t/d pilot-scale grate-type incinerator for municipal solid waste during the co-incineration of industrial solid waste, and the velocity field, temperature field, and the concentration field of pollutants including CO, NO_x, and SO_2 were analyzed during the incineration process. The results showed that the velocity field distribution in the incinerator was similar for incinerating municipal solid waste, industrial solid waste, or a mixture of both, with lower flow velocity in the upper part of the bed and uniform overall flow distribution. The main combustion zone occurred on the first grate, and the addition of industrial solid waste expanded and shifted the high-temperature area, significantly improving the heat transfer coefficient on the furnace wall. The co-incineration of industrial solid waste provided more opportunities for sulfur-containing volatile compounds to react with oxygen, leading to the generation of a large amount of SO_2 in the primary combustion chamber, while the emission concentration of NO_x did not change much. In addition, the results verified in the actual incinerator showed an increase in temperature after mixing industrial solid waste, incomplete combustion of materials in the vertical shaft, a slight increase in SO_2 concentration in the exhaust gas, and little change in NO_x concentration, which is consistent with the simulation results.