The present invention relates to a quasi-resonant controlling and driving circuit and method for a flyback converter. In one embodiment, a controlling and driving circuit for a flyback converter, can include: a differentiation circuit configured to receive a third controlling signal and a drain-source voltage of a main power switch of the flyback converter; where the drain-source voltage is configured to be differentiated by the differentiation circuit to generate a differential voltage when the third controlling signal is active within an interval that the main power switch is shut-off; a valley voltage detection circuit coupled to the differentiation circuit, and configured to receive the differential voltage; and where a valley controlling signal is configured to be generated by the valley voltage detection circuit to achieve quasi-resonant driving for the main power switch of the flyback converter when the differential voltage crosses zero with a positive slope.