After analyzing the data and discussion two main keys for smelting martensitic stainless steel for hydro power were understood. VOD oxygen blowing decarburization technique control and control of gas content. Argon flowrate, ultimate vacuum and temperature have impact on VOD oxygen blowing decarburization technique control. Suction and degassing of liquid steel have impact on control of gas content. According to the knowledge mentioned a- bove, VOD technique had been optimized, which further improves qualified rate of first decarburization of stainless steel casting and Cr alloy recovery. The gas content in liquid steel was decreased and the product quality was en- hanced at the same time, consequently production cost was reduced.