A linear driving system for LED with high power factor including a rectifying circuit receiving an AC voltage and generating a DC voltage to a power supply bus having a protection circuit coupled thereto. The protection circuit includes a detection unit for acquiring a voltage signal based on a power supply bus voltage, and to generate a detection result which indicates undesirable oscillation on the power supply bus voltage. A control unit includes a delay control module connected with the detection unit, and is coupled to the detection unit and for generating a control signal based on the detection result. The delay control module is for outputting a first control signal when undesirable oscillation happens, and outputting a second control signal after a protection period when undesirable oscillation disappears. A switch circuit controlled by the first control signal and the second control signal turns off for the protection period.