An under-voltage protection method is applied in a battery management system. The battery management system includes a control module, an analog front-end unit, a monitoring unit, and a charging and discharging unit. The control module has a system communication function. The control module includes a micro-controller, and an electrically erasable programmable read-only memory connected with the micro-controller. The analog front-end unit is connected to the micro-controller. The monitoring unit is connected to the analog front-end unit. The charging and discharging unit includes a charging switch which is a charging field effect transistor, and a discharging switch which is a discharging field effect transistor. The monitoring unit, and the charging and discharging unit are connected with the analog front-end unit.