Based on exploring quenching mechanism,three types of quenching critical cooling rate models of medium-carbon steel and low-carbon steel and low-alloy construction steel were established,as modified Maynier model,Eldis model and isothermal curve model,respectively. During construction process,regression analysis and Newton interpolation method were used for higher calculated precision. Through comparing and analyzing,the superior one was selected to evaluate the full hardening thickness after quenching. According to hardness analyzing,the deviation between predicted hardness distribution and the experimental value is within 6%. Based on exploring quenching mechanism, three types of quenching critical cooling rate models of medium-carbon steel and low-carbon steel and low-alloy construction steel were established, as modified Maynier model, Eldis model and isothermal curve model, respectively. During construction process Through comparison and analyzing, the superior one was selected to evaluate the full hardening thickness after quenching. According to hardness analysis, the deviation between predicted hardness distribution and the experimental value is within 6%.