Abstract: The nickel-based single crystal superalloy was prepared by medium frequency induction melting and MgO crucible. The content of oxygen, nitrogen and sulfur and the microstructure of the alloy under argon shielded and vacuum melting process were studied comparatively. The impurity removal effects of different processes were analyzed. The effects of extending refining time, adding ceramic filter and adding deoxidizer carbon in vacuum melting process on impurity removal were discussed. The results show that the mass fractions of oxygen, sulfur and nitrogen in argon shielded melted nickel-based single crystal superalloy were all higher than 1× 10^-5, and there was coarse alumina inclusion in the structure. The mass fraction of impurity elements in vacuum melted alloy was less than 1×10^-5, and no large-size inclusions were found in the structure. Compared with argon shielded melting, high vacuum melting could reduce the content of nitrogen in the alloy. Extending refining time could promote the homogenization of alloy composition, and high-power electromagnetic stirring could accelerate the removal rate of nitrogen. Adding ceramic filter removed large size inclusions in the alloy. Further deoxygenation and nitrogen removal was carried out by the reaction of deoxidizer carbon and oxygen.