Abstract: The heat treatment experiment was carried out with the heavy H-beam rolled in the industrial trial as the research object. The effect of cooling rate on the microstructure and mechanical properties of the heavy H-beam flange in the thickness direction was studied. Combined with the continuous cooling transformation curve, the relationship model of microstructure and properties of the heavy H-beam was modified. The results show that when the cooling rate is in the range of 2-4 ℃/s, increasing the cooling rate can increase the pearlite content structure of H-beam, reduce the ferrite grain size, and increase the yield strength, but decrease the plasticity of the material. When the cooling rate is greater than 5 ℃/s, the microstructure is ferrite and bainite. If the cooling rate is further increased, martensite will appear. The calculation results of the modified model are in good agreement with the experimental results, and the prediction accuracy of the modle is high. The pridiction of mechanical properties can be realized by microstructure test.