A method and apparatus for modulating a load by means of control command obtained by varying conduction angle of AC voltage is provided. Under normal operation, conduction angle of AC is approximate to 180 degrees. When a state change command of the load is to be executed, the angle of conduction angle is changed by a conduction angle modulation circuit of control end. After a conduction angle detection circuit of the load end detects the conduction angle, a control unit decodes the information of the conduction angle, and controls the load to perform a corresponding operation. The method and apparatus do not need to add an extra control wiring for the load, and may use the conduction angle of an AC power supply to effectively perform multifunctional modulations on the load with existing power lines, and the defect of a low power commonly found in a traditional dimmer is overcome.