An isolated switching converter includes a transformer, a primary circuit, a rectifying circuit and an optocoupler with a photo-sensitive device and a light emitting device, wherein the light emitting device has a first terminal coupled to an output voltage of the switching converter. A method for controlling the switching converter includes: sensing the output voltage and generating a voltage feedback signal; generating an error amplifying signal based on a reference signal and the voltage feedback signal, and providing the error amplifying signal to a second terminal of the light emitting device; disconnecting the error amplifying signal from the second terminal of the light emitting device if the error amplifying signal becomes lower than a first threshold voltage; and reconnecting the error amplifying signal to the second terminal of the light emitting device when the voltage reference signal becomes lower than a second threshold voltage.