The invention discloses a class-D amplifier and a control method thereof. The gate source voltage difference value of an integration transistor is controlled by controlling an error amplifier to output an appropriate bias voltage signal to keep the gate source voltage difference value above a threshold voltage, so that an MOS (Metal Oxide Semiconductor) capacitor I of the integration transistor always works stably in a strong inversion region. The MOS capacitor of the integration transistor is taken as an integration capacitor of an error integrator, so that the integration capacitor of the error integrator can keep stable. In the class-D amplifier, the chip area can be saved, and the mask layer number in production is reduced. Meanwhile, through design of the class-D amplifier, the harmonic distortion performance and loop stability of the amplifier are enhanced.