The invention discloses a subminiature pre-charging device and a pre-charging method. The device consists of a control unit, a current sensor, a voltage transducer, an IGBT module, a negative temperature coefficient resistor and a lock-up relay. Different voltage platforms are adapted by controlling the duty ratio of the IGBT module, and useless current loss is reduced by using the characteristics of the negative temperature coefficient resistor, so that the volume of the pre-charging device is greatly reduced, locking maintenance is carried out on the output of a contactor, and the reliability of power distribution is improved.