The disclosure relates to a control circuit, a control method and a flyback converter of primary-side feedback control including the control circuit. On the basis of the current sampling signal feedback, the flyback converter of primary-side feedback control is controlled to operate in a constant on time mode when the input voltage is large, and is controlled to operate in a peak current mode when the input voltage is close to a valley. Thus, the peak value of the primary-side current may not become too small because of a decreased input voltage, further avoiding occurrence of an error sampling after a blanking time due to excessive variations in demagnetization time.