An auto-controlling power saving system for solar energy street lamps includes at least one street lamp, each street lamp having a light source at an upper end thereof; a battery set; at least one solar plate installed at an upper end of the light source for absorbing solar energy; the absorbed solar energy being converted into electric power which is transferred to the light source for lighting up the light source or is stored in the battery set; a main controller for controlling all electric powers of the elements of the system for power management; the main controller controlling actuation, de-actuation and illumination of all street lamps; the main controller being connected to the battery sets of the street lamps and the related elements used; the main controller having a plurality of power control modes for power management and illumination control of the street lamps.