The invention provides a method for detecting the Austenitic coarsening temperature of steel. The method comprises the following steps: preparing a detection test piece; placing the detection test piece into a crucible, placing the detection test piece and the crucible into a metallographic-phase heating furnace, repeating operation of vacuumizing and introducing argon for three times, and continuously introducing high-purity argon with the purity of more than 99.999% into the metallographic-phase heating furnace to serve as protective gas during heating of the detection test piece; continuously heating the detection test piece to 800 DEG C at the speed of 150 DEG C/min, maintaining constant temperature for 120 seconds, and continuously heating to 1,350 DEG C at the speed of 15 DEG C/min, wherein in the heating process, a high-temperature laser imaging system above the metallographic-phase heating furnace continuously acquires Austenitic grain size photos of the detection test piece at the temperature interval of 0.1 DEG C, and the temperature at which Austenitic crystal grains start to grow up serve as the Austenitic coarsening temperature. The invention provides a method for detecting the Austenitic coarsening temperature of steel, which has the characteristics of short consumed time and precise temperature detection.