The microstructure parameters of steel can characterize a variety of physical properties. Steel strips and key pressure vessels in service need to be tested online for their microstructure parameters. This paper analyzes the on-line detection method of metal material microstructure. The research status and existing problems of electromagnetic methods ( hysteresis loop, magnetic Barkhausen noise, multi-frequency eddy current, harmonic analysis of tangential magnetic field strength) and ultrasonic methods (sound velocity method, attenuation coefficient method, nonlinear ultrasonic method and combination of multiple ultrasonic parameters ) in microstructure detection of metal materials are summarized. The relationship between the physical properties of metal materials and the microstructure parameters and the unclear relationship are discussed, and the development potential and direction of metal microstructure detection are prospected.