The invention discloses a heat treatment method for improving mechanical properties of TRIP steel of a Fe-Mn-Al-C system, and belongs to the field of heat treatment of new materials. The heat treatment method comprises the following steps of (S1) smelting: preparing a manganese block, an iron block, an aluminum block and carbon powder according to alloy components of the TRIP steel, and smelting in a protective gas atmosphere; (S2) forging: heating and insulating a smelted steel ingot, forging into a steel billet, and performing air cooling to the room temperature; (S3) performing hot rolling:heating and insulating the billet in a heating furnace, rolling into a hot rolled plate, and performing air cooling after rolling; and (S4) performing quenching and tempering treatment: heating the steel workpiece of the hot rolled plate to the quenching temperature at preset speed, performing water quenching on the workpiece to the room temperature, then heating and insulating, and subsequently,performing air cooling to the room temperature. According to the heat treatment method, the defects of high heat treatment cost and complex process of the TRIP steel in the prior art are overcome, quenching and tempering processes are adopted, compared with critical heat treatment and isothermal bainitic transformation and austenitic inversion, the method has the advantage of simplicity in operation, and the performance is better than that of traditional hot rolling TRIP steel.