The invention provides a street lamp loss reducing and power saving device which comprises a transformer high-voltage switch controller, a low-voltage switch controller and a power controller, wherein the power controller is connected with the high-voltage switch controller and the low-voltage switch controller respectively; and the high-voltage switch controller and the low-voltage switch controller are connected with a high-voltage switch and a low-voltage switch respectively. The device controls a street lamp transformer to run/stop according to the set sequence, namely that the high-voltage switch of the transformer is firstly put into operation, and then the low-voltage switch is put into operation to supply power to the street lamp at night. In the daytime, the low-voltage switch is firstly switched off to stop power supply to the street lamp, and then the high-voltage switch is switched off to stop power supply to the transformer, thereby reducing the loss of electric energy of a power grid. In order to save power, the two switches on the low-voltage side of the transformer control the two sides of a road or perform cross control at an interval of a street lamp respectively, thus the street lamps on the road are turned off at 12 p.m. in advance, namely that the illumination of some street lamps is reduced when people and vehicles are few at late night so as to achieve the purpose of saving power. The application of the device has broad market prospects.