The invention relates to an under-voltage protection circuit. The under-voltage protection circuit comprises a voltage-dividing sampling circuit. The sampling point of the voltage-dividing sampling circuit is connected with the control end of a first switch tube (Q11) through a first voltage-stabilizer tube (ZD11); the output end of the first switch tube (Q11) is connected with a third switch tube (Q13) through a second switch tube (Q12); and the third switch tube (Q13) is used for cutting off or conducting a DC working power source. The under-voltage protection circuit only employs switch tubes, voltage-stabilizer tubes, resistors and a capacitor, the structure is simple, the cost is low, the miniaturization is easier, the circuit is realized completely by hardware, and the safety and reliability are high.