The invention discloses an energy-saving power supply method for street lamps, which comprises the following steps: acquiring an output voltage value of an energy-saving terminal for street lamps; determining a rated voltage value of the energy-saving terminal for street lamps according to the acquisition time of the output voltage; comparing the output voltage value with the rated voltage value;and when the output voltage value is greater than the rated voltage value, reducing the output voltage value until the output voltage value is not greater than the rated voltage value, and then, determining the reduced output voltage value as an input voltage value of a street lamp. The method is implemented through the following steps: continuously acquiring the output voltage value of the energy-saving terminal for street lamps; comparing the output voltage value with the rated voltage value in a time-output voltage list; and when the output voltage value is greater than the rated voltage value, reducing the output voltage value of the energy-saving terminal for street lamps until the output voltage value is not greater than the rated voltage value, and then, determining the reduced output voltage value as the input voltage value of the street lamp. Thus, with the gradual reduction of traffic streams and streams of people on highways, the output voltage value of the energy-saving terminal for street lamps is reduced, i.e. the input voltage of the street lamp is reduced, thereby reducing the power consumption of the street lamp, and reducing the energy loss of the steel lamp.