Abstract: In this paper, the acoustic emission technology is used to perform the martensite phase change monitoring experiment under continuous cooling conditions for three kinds of materials, 45 steel, GCr15 steel and T12 steel, and to implement the time-frequency characteristic research based on acoustic emission parameter distribution and the waveform feature of the phase change. The results show that GCr15 steel has obvious phase transformation characteristics of isothermal martensite, 45 steel and T12 steel have the characteristics of variable temperature martensite, and the acoustic emission signal amplitude and energy in lamellar martensite are higher than those in plate strip martensite, and the signal in lamellar martensite has a wide range of frequencies.