When the power transformer in partial discharge test, if the test equipment (voltage regulator, intermediate transformer, etc.) ontology partial discharge is big, it will severely affect the quality of testing, and even cause false identify.How to correctly identify partial discharge from the power transformer or from the test equipment itself, it is very important for the test personnel. This paper introduces to use the idle 220kV circuit breaker in parallel capacitor to cleverly find out in the whole process of partial discharge from the test equipment itself.