The “Fat-finger” event which happened in Everbright Securities on August 16 was seemingly an accident. However, the event exposed many internal control deficiencies of Everbright Securities. This essay makes an analysis of the deficiencies of Everbright Securities in internal environment, risk assessment, control activities, information and communication, and internal supervision. Furthermore, it elaborates on the cause of the “Fat-finger” event. It is hoped that the essay can give some enlightenment to securities companies on internal control construction.