To improve the utilization rate of external environmental information of power grid fault diagnosis method and to realize the analysis of the fault causes on the basis of fault identification

we design a method for power grid fault identification and cause analysis in which external environmental information is taken into consideration. First

to solve the problem of solidified weight of fault diagnosis criterion

we analyze the difference and credibility of the alarm information of the circuit breaker and the protection. The analytic hierarchy process（AHP） weight analysis method is used to give greater weight to the information with higher credibility

so that the impact of wrong alarm information can be reduced

and the accuracy of fault diagnosis can be improved. Secondly

for the lack of fault cause analysis

environmental information（the type of information and its alarm level） is introduced as the fault cause analysis criteria

and the fuzzy comprehensive evaluation（FCE） method is used to evaluate the damage caused by the environmental factors to the grid and to further determine whether the fault is caused by environmental factors; thereby

the further identification of fault causes will be carried out. Finally

simulation verification is carried out by establishing the failure calculation examples in the case of protection action alarm information under-reporting and false-reporting

as well as scenarios of circuit breaker refusing to operate and mis-operating. The research results show that the proposed method can effectively use a variety of fault-related information

and can be adopted to improve the accuracy of fault identification results and to further analyze the cause of faults. Therefore

the method can be adopted to effectively improve the efficiency of power grid fault diagnosis and ensure the reliability of power supply.