A calculating method for oxygen fugacity of paragenetic clinopyroxene-garnet pair is established on the basis of data obtained from the major types of skarn ore deposits in combination with experimental results of Ca-Fe-Si-C-O system and by means of thermodynamic calculation for solid solution of the paragenetic minerals. A study of major types of skarns in China suggests that different metallizations and skarns occur in different environments of oxygen fugacity and show different variation trends of oxygen fugacity and diverse effects of temperature-oxygen fugacity. The paragenetic clinopyroxene-garnet pair is as effective indicator for the oxygen fugacity and acidity of ore--forming fluids and helps to discriminating between metallization types of skarns.