12Cr1MoV steel was heated to different temperatures (650, 750, 850, 950, 1 050,1 150 °C) for 3 h and then air-cooled and water-cooled, respectively, to simulate the burning process at fire sites. The effect of the burning temperature and cooling way on the microstructure and mechanical properties of the test steel was studied by metallographic inspection, small punch tests, tensile tests and hardness measurement. The results show that when the fire temperature was not higher than 750 ℃, the microstructure of the test steel mainly consisted of ferrite, pearlite and carbide under air cooling and water cooling, and the change of strength, percentage elongation after fracture and hardness was small with the burning temperature. Under air cooling, when the burning temperature was higher than 750 ℃, the test steel experienced an increase in grain size and pearlite conten, leading to an increase in strength and a decrease in percentage elongation after fracture. Under water cooling, when the burning temperature was higher than 750 ℃, martensite appeared in the structure of the test steel. The content of martensite increased with the burning temperature rising, resulting in an increase in strength and hardness and a decrease in percentage elongation after fracture of the test steel.