A compulsory charging and protective circuit for secondary battery after being over discharged is disclosed. The circuit includes a circuit conducting switch, a releasing unit, a triggering unit and a comparing unit. When the secondary battery is over discharged, a temporary electrical connection is provided by the present invention. The loop of the secondary battery and a charger keeps. When the secondary battery recovers from abnormal status, the temporary electrical connection is called off so that the secondary battery can keep normal operation. Thus, when the secondary battery is under over-discharge, it doesn't have to be unloaded for repair to settle the issue. Maintenance costs can be saved.