The invention discloses a method for supplying power to a low-voltage system by using a rectification dead zone. The power is input into a microprocessor through zero-cross detection, the time of two zero-cross points is detected, the grid frequency is calculated, the minimum voltage after filtering is calculated with the formula shown in the specification according to the magnitude of a circuit filter capacitor, the phase angle of the minimum voltage is inversely calculated according to the circuit requirement with the formula Uu=Um*sin(omega t+phi), and the microprocessor sends a switching signal through IO to turn on a switch to charge the low-voltage system in the period from maximum voltage Umax to minimum voltage Umin. With the adoption of the method, power is supplied to the low-voltage system by using the dead zone, the space and the cost are greatly saved, and the power factor of a product is effectively increased.