The insulation defects can be found out and the operation state can be known accurately by using on － line detection technology． A typical case of partial discharge in 10 kV switchgear is described． By using transient earth voltage ( TEV) detection technology，acoustic emission ( AE) detection technology，and ultra － high frequency ( UHF) detection technology， the partial discharge signal in switchgear is detected． Through signal analysis and outage detection，the main reasons are found out and the improvement measures are put forward． The obtained results can provide a reliable guidance for the detection and improvement measures of partial discharge in switchgear．