A pulse-width-modulation control circuit of a switching-mode power converter with a primary-side feedback control is disclosed. The switching-mode power converter includes a transformer, a power switch, a current sensing resistor and the pulse-width-modulation control circuit. The transformer includes a primary-side winding, a secondary-side winding and an auxiliary winding. The pulse-width-modulation control circuit includes a sample and hold circuit, a transconductor circuit, an error amplifier and a pulse-width-modulation generator.