In this paper, the synthesis process of quetiapine key intermediate chloride(11-chlorodibenzo [b, f] [1, 4] thiazapine) was optimized.10 H dibenzo [b, f] [1, 4] thiaaza-11-one and phosphorus oxychloride were used as raw materials, toluene as solvent and N, N-dimethylaniline as catalyst, The target product chloride was obtained by chlorination reaction.The yield and purity of quetiapine were 90 % and 99.5 %, resp.The process optimizes the feeding amount of phosphorus oxychloride, greatly improves the product yield, reduces the pressure for the later treatment of phosphorus containing wastewater, and is suitable for industrial production