The invention provides a power converter and a control method thereof. The power converter includes a transformer, a primary side control circuit, and a secondary side control circuit. A primary side of the transformer receives the input voltage, and a secondary side of the transformer generates the output voltage; the primary side control circuit controls a current switch and switching thereof of a primary winding; the secondary side control circuit is arranged on the secondary side of the transformer; and the secondary control circuit includes a locking an storing circuit. When a failure occurs, the locking and storing circuit clamps a feedback signal and maintain the clamped state; when the feedback signal is clamped, the primary side control circuit stops switching the current switch of the primary winding, and when the output voltage is lower than a preset locking and storing voltage value, the locking and storing circuit releases the feedback signal. The power converter can continuously control the feedback signal while the output voltage is pulled down without arranging a charging pump circuit for improving the working voltage of the secondary side control circuit.