Owing to the features of high sensitivity and good anti-jamming capability,Ultra High Frequency (UHF) is widely used in the field test of Gas Insulated Switchgear (GIS).In order to explore the relationship between UHF signals and apparent discharge magnitude,this paper established combined measurement system,partial discharges data on metal protrusions under pressures from 0.3 to 0.5 MPa were collected.The cumulative energy of UHF signals was extrated to conduct a correlation analysis with apparent discharge magnitude.It is concluded that the singnal energy has a linear relationship with the square of discharge quantity unedr different pressure.The linear slope has a strict relation with pressure.The results can lay a foundation on the calibration of UHF signals.