Fuel tanks of civil aircraft are generally designed with a symmetrical layout, where internal leakage can result in difference in fuel quantities between the two sides. During flight, if the fuel imbalance grows to a certain threshold , the fuel imbalance alarm will be triggered. It requires the crew to eliminate the abnormal alarm information operate according to the abnormal procedures in the flight crew operation manual, which affects the crew's attention and is not conducive to flight safety. For the fuel imbalance alarm information of a certain type of aircraft during route operation. Firstly,the basic structure of the fuel system is introduced. Then, the causes of the fuel imbalance alarm were analyzed based on fault tree and enhanced airborne flight recorder (EAFR) data. Finally, temporary solutions that do not affect route operation and subsequent optimization suggestions are put forward. To provide the reference for troubleshooting and aircraft design optimization.