In recent years, Ultraviolet(UV) detection technology in corona discharge detection and defect diagnosis of partial discharge has been widely used. However, electro-optic characteristics and quantitative relationship between corona current and UV emission intensity in the process of corona discharge are virtually worth studying deeply. With different Alternating Current(AC) voltage and different humidity, corona current and UV pulse number are measured. It is shown that corona current and pulse number rise with the voltage mounting up and approximately decline with humidity increasing. In addition, further discusses about the quantitative relationship between corona current and UV pulse number are implemented by using transfer function. The experiment results, under the conditions of different AC voltage and different humidity, indicate that transfer function maintained between 2.4～3.6 changes little. UV pulse number, therefore, can be used to characterize corona current intensity. The conclusions above are significant for characterizing the level of corona discharge directly by UV emission intensity, and are helpful for improving the accuracy of defect diagnosis.