The micro energy harvester based on a polycrystalline silicon nanowire rectangular array and a nano PN junction of the present invention is composed of a photocell and a thermoelectric energy harvester. A ZnO film is prepared by a gel spin coating method to obtain a nano-PN junction of the photocell. The thermoelectric energy harvester is formed by a nanowire rectangular unit rectangular array. Anano thermocouple is obtained from the nanowire rectangular unit by a deep ultraviolet lithography process. Compared with a conventional thermoelectric photoelectric energy collector, the polycrystalline silicon nanowire has much lower thermal conductivity than a conventional bulk material, and has high thermoelectric conversion efficiency. The nano thermocouple pairs are interconnected by gold wires and the nanowire rectangular units are interconnected by gold wires. The energy collected by the photocell and the thermoelectric energy harvester is output through a thermoelectric output pad anda photoelectric output pad. The collected energy is ultimately stored in a rechargeable battery. The electrical energy in the rechargeable battery can supply power to wireless sensing nodes.