In order to apply laser induced breakdown spectroscopy (LIBS) to the study of the features of heating surface metallic materials, 12Cr1MoV steel samples with different grain sizes (class 7, 6, 5 and 4) are selected as the objects. Under different experimental conditions (both laser energy and spot diameter), the relevance between spectral characteristics and different classes of 12Cr1MoV grain size is investigated. The results show that it makes a well correlation between Fe or Cr spectral intensities and different grain size classes in different enery conditions with the spot diameter of 206 μm. It is found that in the condition of 100.6 mJ laser energy and 206 μm spot diameter, the fitting degree is 0.987 which is better than the fitting effect directly obtained by the spectral intensity, when analyse the ratio of Fe ion line and atomic line.