Inclusions are an important factor for steel performance. Many methods can be used to analyze the size and component. But no report was found that inclusion size and concentration was determined simultaneously. The metallographic microscope and SEM require fine polishing sample surface in inclusion analysis. Steel samples should be grinded at 800 mesh grinding paper and polished to mirror surface, and it is a time-consuming process. LIBS can analyze the inclusion size distribution over 1 μm and content average in steel and sample surface can be ground by over 80 mesh grinding paper, the mirror surface is not needed. When LIBS was used analyzing steel samples, if burn shot contains soluble element and its inclusion, homogenized soluble element in the matrix Fe presents in Gaussian distribution, inclusion as an “element concentrated area” yields high intensity than soluble element and additive to soluble element intensity. Inclusion intensity which was separated from the total intensity contains information of inclusion size and average inclusion concentration. When inclusion was excited, the enrichment element comes to the plasma and emit hight light intensity. Analyzing the steel samples which contain Al2O3 and MnS inclusions, the inclusion size and area were obtained and make a correlation with the LIBS inclusion intensity. The results show that the inclusion area and LIBS inclusion intensity are linear correlation, the diameter of globular inclusion and LIBS inclusion intensity are parabolic correlation. Average inclusion concentration which comes from multi-shot and LIBS inclusion intensity is linear correlation. Formulas （1）, （10）, （20）were given which using the same intensity data to analyze the inclusion size, area and concentration. The principle for simultaneous analysis of inclusion size (or area) and average content in steel by LIBS are explained. The Al2O3 inclusion in steel samples is analyzed and verified. The Al2O3 inclusion content analysis results and formula are coincided each other.