In order to determine the severity of partial discharge, precise calibration in the amount of discharge is required for the application of ultra-high frequency in Cable and GIS partial discharge monitoring. In this paper, a method for the calculation of partial discharge based on Friis transmission equation is presented, which integrates partial discharge source as a transmitting antenna modeling and introduces Friis transmission equation to make the calculation equivalent to the transmission process of the antenna. By taking the fourth-order Hilbert fractal antenna resulting from HFSS simulation as receiving antenna model, and utilizing partial discharge tests, calculation and analysis, the conic relationship between partial discharge and the energy of receiving UHF signals is determined.