Various defects are accompanied in steel heat treatment process. Heat convection and steam film cause non-homogeneity of heat transfer. The technique that the quenchant is put into stirring in order to prevent these heat treatment defects are proposed. In addition, the heat transfer coefficient is identified in order to carry out the simulation promoted recently. The purpose of this paper is to propose a method of identification of heat transfer coefficient and verify effect of the quenchant on internal structure and mechanical behavior. Here, the stirring quenching experiment was carried out using ring specimen of carbon steel SCM 420. Then, heat transfer coefficient was identified from measured temperature on surface of the specimen. The heat transfer coefficient was input into simulation data, and the calculation using the finite element method was carried out. Simulation results were compared and verified with the experimental value, and identification result of the heat transfer coefficient and effectiveness of the stirring of quenchant were confirmed.