In order to reduce or even completely eliminate the high concentration of H2S acid gas directly into the air combustion, the formation of air pollution gas SO2. This paper introduces the original design flow of acid gas in the second phase of the low-temperature methanol washing unit in Double-A workshop of Wei nan, Shan Xi Province, the principle of split range control, and the regulation mode and process of acid gas pipeline after transformation.The results show，that the operation condition is good and the environmental protection effect is obvious after the transformation, which not only achieves the zero emission of acid gas, but also achieves the purpose of increasing the sulfur production, it is a transformation project worthy of promotion.