The article, based on the running of Haolong Thermal Electricity Plant, enumerates the circuit breaker malfunctions caused by a second return circuit trouble, analyzes the causes and offers the corresponding strategies against them.

According to analyzing two cases for secondary intermittent fault causing high frequency protection mulfunction,the paper finds out the reason of the mulfunction and establishes preventive measures,it has a certain reference for the fault searching and treatment in microcomputer protect operation.