Underground wireless sensor nodes have limited energy. Hence, energy harvesting technology can be used to convert underground environmental energy into electrical energy to supply power to the sensor nodes, thus extending the life cycle of wireless sensor nodes. The light intensity in the low light environment of the underground roadway is tested and analyzed. The results show that the light intensity is 50-170 Lux in the range of 1-2 m from the light source, which is in line with the working range of photoelectric materials such as amorphous silicon and perovskite. It verifies the feasibility of converting the underground low light energy into electrical energy. An underground micro energy harvesting device is designed by using 30 cm×40 cm amorphous silicon photovoltaic panels, BQ25505 power management chip and lithium batteries, which can convert the underground low light energy into electrical energy and store it. According to the characteristics of discontinuous energy in the underground environment, an energy caching mechanism is designed. In this mechanism, a rechargeable lithium battery with smaller capacity is used as the energy caching battery, and a lithium battery with larger fixed capacity is selected as the backup battery. When the voltage of the rechargeable lithium battery reaches the design value, the sensor node is powered by the rechargeable lithium battery. And when the voltage is insufficient, the backup battery is switched to supply power to ensure the normal operation of the wireless sensor node. The micro energy harvesting device has been tested in the laboratory and underground. The results show that the device can output milliwatt power with the light intensity above 50 Lux. When the underground light intensity reaches 170 Lux or more, the device can use the converted energy to power the low-power wireless sensor node without backup battery. When the light intensity does not reach 170 Lux, the energy caching mechanism coordinates the rechargeable lithium battery and the backup battery to power the wireless sensor node, which improves the node life cycle effectively.