Abstract: The effects of process and different calcium treatment methods on Ca/S and inclusions in steel and the effects of low superheat match and dynamic soft reduction technology on macrostructure quality of billets of acid resistant steel Q345R smelting by “BOF-LF-RH-CC" process are analyzed. Research shows that"LF + RH + calcium treatments" process can significantly increase the Ca/S in molten steel and reduce the size of A and B inclusions in steel. As calcium treatment is carried out after RH breaking vacuum, the class 2. 0 Ds inclusions appear in finished plate, but the size and quantity of these inclusions can be reduced by prolonging the soft blowing time. With LF/RH two steps calcium treatments process and soft blowing time for 16 ~20 min after RH calcium treatments, the inclusion size of B, Ds, D can be controlled ≤1.0 rating and the inclusion size of A,C can be controlled ≤0.5 rating in steel plates. Core segregation of billet macrostructure rating is C type 1.0 by 5 〜12℃ superheat casting match and dynamic soft reduction technology, the segregation rating of each elements is low. Using the process, the composition, inclusions and macrostructure quality can meet the acid resistant steel Q345R requirements.