The invention provides a power-on and power-off control method and device for medium-low voltage and an electronic device. The method comprises the following steps: when detecting power-on operation,sending a pre-charging instruction to a DCDC converter such that the DCDC converter converts low voltage into high voltage in order to carry out pre-charging operation; when detecting that pre-charging operation is finished, sending a pull-in request instruction to a battery management system BMS such that the BMS pulls in a power battery relay to perform power-on of medium-low voltage. In the technical scheme provided by the embodiment, the DCDC converter converts low voltage into high voltage, thereby achieving a pre-charging function of a medium-low voltage system. While safety is considered, cost is effectively lowered. Additionally, after detecting power-on operation, the power battery relay is automatically pulled in after pre-charging is finished without trigger of a specific event.The time between power-on operation and starting of an engine is shortened, thereby enhancing user experience.