Current detection function is the key factor to sense signal of switches and improve the reliability, cost and component size of the power factor correction system. The conventional current detection method is based on external shunt resistor measurement detects the current passing through shunt resistor which series between switches and ground to determine whether the switches overcurrent fault occurs and control the duty cycle on PFC converter. The current sensing control circuit will be implemented in this thesis and directly senses the on-resistance of the power MOSFET as the signal sensing resistor, which can eliminate the external shunt resistor, thereby the BOM cost and circuit can be reduced. On the other hand, the sensing signal also can avoid distortion and malfunction due to the parasitic effect. Finally, use the LTspice 4.23 software to simulate PFC construction which input voltage:85 VAC ~ 230 VAC, the output voltage of 400 VDC and 300 W load.