The present invention provides a method of simultaneously recycling plastics and detoxifying chromite ore processing residue with residual heat from a steel slag. By heating and gasifying plastics with steel slag, followed by catalytically split-decomposing the plastics with catalysts such as chromite ore processing residue, the plastics are thoroughly converted into a energy gas under water vapor gasification. The surface coking of Chromite Ore Processing Residue is avoided. Meanwhile, the energy gas reduces Cr6+ in Chromite Ore Processing Residue into Cr3+, and the energy gas is cooled, and CO2 and Cl in the energy gas are adsorbed by alkaline substances in Chromite Ore Processing Residue. With this method, chromite ore processing residue is detoxified, and steel slag is cooled, furthermore, energy is saved and a energy gas is obtained.