Abstract: Based on the information of decarbonization reaction in a convertor continuously obtained with gas analysis technology, the critical carbon content at the decarbonization rate change point,C_d, in BOF blowing process was researched by back-calculation method. The results show that the effect of bath stirring energy on the critical carbon contentC_d is very obvious near the refining end point, and the critical carbon contentC_d decreases with increasing stirring energy due to the increase in bottom blowing flowrate; but when the stirring energy is greater than a certain value, the influence of bath stirring energy on the critical carbon contentC_d is very small. Top oxygen blowing flowrate has important effect on the critical carbon contentC_d for a top blowing converter, and with the increase of oxygen blowing flowrate the critical carbon contentC_d decreases.