The invention relates to a battery power supply device and method for a downhole measuring instrument. The device comprises an external signal transmitting module, an interface unit, battery pack, anelectronic switch and an MCU (microprogrammed control unit) and is characterized in that the battery pack, the electronic switch and the MCU are arranged inside the downhole measuring instrument, theexternal signal transmitting module is connected with the electronic switch and the MCU through the interface unit, and the battery pack is connected to the MCU through the electronic switch; the interface unit is used for providing a battery turn-on excitation signal, a battery turn-off excitation signal and a communication signal transmitted by the external signal transmitting module for the electronic components inside the downhole measuring instrument; the electronic switch is used for achieving the power supply turn on and turn off of the battery pack; the MCU is used for controlling theelectronic switch to operate according to the received battery turn-on excitation signal and the battery turn-off excitation signal so as to turn on and turn off the battery pack. The battery power supply device has the advantages that communication with the interior of the instrument is achieved through an instrument shell, the battery pack can be controlled to turn on and turn off, and the battery power supply device is simple in field operation, low in instrument manufacturing and maintaining cost, high in reliability and high in high-temperature resistance of circuits.