Abstract: Based on the conversion data of Leeb hardness and Brinell hardness for high temperature pipe material of T/P91 steel and T/P92 steel in thermal power plant, and according to the physical meaning of the two kinds of hardness and the mechanical properties of the material, a simplified stress-strain model was established. The difference in conversion of Leeb hardness and Brinell hardness between T/P91 steel and T/P92 steel was analyzed, and this difference was explained by physics. It was also pointed out that the Leeb hardness was limited by the test conditions, and influenced by the physical and mechanical properties of the materials at the same time. The conversion of Leeb hardness and Brinell hardness for different materials should be based on the experiments, and it was a result of big data statistics and analysis. The more data accumulated, the more accurate the conversion results were.