The invention discloses a single-lamp energy-saving controller for street lamps and a method thereof. The single-lamp energy-saving controller comprises a central processor, as well as a street lamp working-status collection interface, a street lamp current/voltage acquisition interface, a multi-lamp control expansion interface, a power carrier communication interface and a power-cutback ballast control interface which are respectively connected with the central processor. The power line carrier communication interface is connected with a spread spectrum power carrier communication module; the power-cutback ballast control interface adopts strong/week current isolation and two-stage drive and receives switching value signals output from the central processor. The method includes the following steps of: device parameter initializing, state detection, new data detection, received new data processing, timing control processing detection, timing control processing and watchdog removing. The single-lamp energy-saving controller does not cause the pollution of the power grid environment or other adverse effects; simultaneously, based on the strong capacity of resisting power grid disturbance, the single-lamp energy-saving controller can carry out power cutback operation according to the preset time sequence, when in use separately, thereby achieving the energy-saving effect.