Abstract. Thinning features of 22MnB5 in hot forming process were investigated by simulation of AUTO-FORM on the base of verification of the results in a published paper. The thinning of 22MnB5 in the isothermal forming process was calculated and the effect of temperature on cracking was evaluated. A mathematics model of forming limit, which is called FLE (Forming Limit Equation), is recommended to predict the cracking of the sheet in the hot forming process in stead of FLD (Forming Limit Diagram). And effect of other parameters, i.e. blank holding force, friction coefficient, thickness of sheet and strain rate, was also investigated.