External ultra-high-frequency（UHF）sensor is the main measure to achieve live partial discharge detection of GIS.It is of great significance to analyze the influence of insulating spacer of GIS and the pouring port structure on leakage characteristics of UHF signals.The leakage characteristics of the UHF signals are simulated and actually measured on the basis of the port coefficient method.The difference of leakage characteristics between the insulating spaces and without metal ring is observed.Then

the influence rule of the shape and size of pouring port are analyzed and the characteristics of UHF signal internal and external UHV GIS are tested by pulse injection method.The results show that the frequency band of leakage port parameters obtained by the simulation is identical to that of the experimental results.The leakage frequency band of the spacer without metal ring is related to the number of bolts and increases with the number of the bolts.The electric field distribution at the spacer is that the electric filed component which is perpendicular to the insulating spacer is the largest and the electric field between the middle positions of two bolts is maximum.The leakage frequency band of the insulating spacer with metal ring is related to the shape and size of the pouring port.For the rectangular pouring port

the basic resonance frequency becomes smaller as the length of the pouring port increases.For the circular pouring port

much more electromagnetic wave leaks with the increase of the radius of the pouring port

the resonance frequency point of the Spcurve is more dense and the amplitude of the resonance also becomes larger.