A sampling circuit of the power converter according to the present invention comprises an amplifier circuit receiving a reflected voltage for generating a first signal. A first switch and a first capacitor are utilized to generate a second signal in response to the reflected voltage. A sample-signal circuit generates a sample signal in response to a falling edge of a switching signal. The switching signal is generated in accordance with a feedback signal for regulating an output of the power converter. The feedback signal is generated in accordance with the second signal. The sample signal is utilized to control the first switch for sampling the reflected voltage. The sample signal is disabled once the first signal is lower than the second signal. The sampling circuit precisely samples the reflected voltage of the transformer of the power converter for regulating the output of the power converter.