An abnormal discharge alarm device is applied in a steam trap. The steam trap is installed in a pipeline of a steam system. The abnormal discharge alarm device includes a power generation component and a control circuit. The power generation component receives a fluid discharged from the steam trap and generates a self-generated electric power. The control circuit receives and detects the self-generated electric power to obtain a detection result. The control circuit sends an alarm signal when the detection result is greater than a predetermined threshold value. In addition, the abnormal discharge alarm device may further include a monitoring unit. The control circuit transmits the detection result to the monitoring unit. The monitoring unit obtains an updated threshold value according to accumulated detection results, and determines whether to send an alarm after comparing the updated threshold value with a real-time detection result.