The invention discloses economical high-aluminum and low-silicon TRIP high-strength steel for automobiles and a preparation method of the TRIP steel, and belongs to the technical field of production of high-strength steel for automobiles. The TRIP steel comprises the components of, by mass, 0.15-0.25% of C, 0.1-0.5% of Si, 1.5-3.0% of Al, 1.5-2.5% of Mn, 0.1-1.0% of Cu, 0.01% of P and Lt, 0.005% of S and Lt and the balance Fe. The preparation method comprises the following steps of smelting, pouring, forging, heat preservation, hot rolling, thatching, acid pickling, cold rolling and annealingtreatment. Micro-alloy elements contained in the steel are less, so that the steel is economical and beneficial for being recovered; Si is partially replaced by Al, the ductility is improved, and thegalvanization performance of a cold rolled steel plate is improved; a small quantity of Cu is added, the defect of Al at the aspect of strength is made up through solid solution and precipitation strengthening, and the extension strength is improved. By adopting annealing in a two-phase area and heat preservation in a bainite area in the heat treatment technology, a cold rolled plate with the extension strength being larger than 780 MPa, the ductility being over 25%, the maximum ductility reaching 30% and the plate shape and the surface quality being good is obtained. The temperature of the bainite area is higher than 460 DEG C so as to be matched with the galvanization technology to achieve integration of annealing and galvanization, and thus the high-strength galvanized plate for the automobiles is produced.