Detailed thermodynamic analysis of the chlorination reaction of carbonized Pangang BF slay is carried out It is pointed out that oxygen taken part in the chlorination reaction is an important condition of selective chlorination of TiC. Not only could the consumption of chlorine be decreased, but could the residue after chlorination be utilized as well. Heat equilibrium of the chlorination of carbonized BF slag at low temperature and of the carbochlorination of high grade titaniferous slag is calculated and compared. Solving the problems of heat equilibrium and local superheat of large-scale chlorination equipment as well as the controllability of chlorination reaction is the key to decide whether the low temperature chlorination of carbonized BF slag will succeed or not.