The microstructures of 30Mn20Al3 non-magnetic steel after different finishing temperature and cooling rates have been studied by multi-pass compression test in a thermal-mechanical simulator. The results show that the microstructure of this steel is totally of austenitic with amounts of twins. At the same cooling rate, larger amount of thicker twins appear when lowering finishing temperature. The austenite grain size is related to finishing temperature and cooling rate. The critical temperature of austenite recrystallization is determined as 950~1000°C. When the finishing temperature is about 1000°C and cooling rate higher than 15°C/s, fine and uniform austenite grains can be obtained.