The invention relates to a scattering parameter-based partial discharge ultrahigh frequency detection system field check method. The method comprises the following steps: 1) allowing two adjacent ultrahigh frequency sensors on GIS and a GIS structure between the sensors to be equivalent to a two-port microwave network; 2) acquiring the scattering parameter S21 between the two adjacent sensors installed on the GIS by researching the scattering parameter of the two-port microwave network, determining the mean of transmission coefficients in an effective detection frequency band of the ultrahigh frequency sensors, and further realizing field check of an ultrahigh frequency partial discharge online detection system. Before checked, the operating state of a microwave network analyzer can be determined by measuring the scattering parameters S11 at ports where the two ultrahigh frequency sensors are positioned and combining the characteristics of the sensors. The check method disclosed by the invention is small in measuring error, high in detection sensitivity and high in anti-jamming capability and provides a reference base for field check of an ultrahigh frequency partial discharge online monitoring device.