A loading system and a controller thereof are disclosed. The controller includes an adjustable triangle wave generator, an error signal generator, and a pulse signal generator. The triangle-wave generator is adapted to perform an amplitude and frequency operation according to the reference voltage and the feedback voltage for generating an amplitude-frequency adjustable triangle wave according to a variation of the feedback voltage. The error signal generator is adapted to perform an error operation according to the feedback voltage and the reference voltage for outputting an error signal. The pulse signal generator is adapted to receive and compare the error signal and the amplitude-frequency adjustable triangle wave for outputting a pulse controlling signal for the loading system.