The pearlitic heat resistant steel 12Cr1MoV is chosen as the research object. Different microstructure samples are made by different heat treatment processes. The microstructures of these samples are pearlite and ferrite, lath martensite and a small amount of residual austenite, martensite and sorbite. The spectral intensity of laser-induced breakdown spectroscopy (LIBS), plasma temperature, electron density and the relation between microstructure and the ionic to atomic spectral line intensity ratio of Fe element are compared and analyzed. The experimental results show that the spectral intensity of martensite is strongest, the spectral intensity of ferrite and pearlite is almost similar to that of lath martensite and a small amount of residual austenite, the spectral intensity of sorbite is weakest. The plasma temperatures of samples are almost consistent. The electron density of martensite is the maximum and those of remaining samples are similar. There is a certain correlation between Fe ionic and atomic line intensity ratio and microstructure, which indicates that LIBS has the potential to be used as detection tool of microstructure variation of heat transfer surfaces in power plant boilers.