The invention discloses a low-pass filtering type voltage-stabilizing protection system for mains supply. The low-pass filtering type voltage-stabilizing protection system is characterized by mainly comprising a transformer T, a diode rectifier U, a triode VT3, a resistor R7, a capacitor C1, a capacitor C3, a diode D2, a diode D3, a power supply trigger circuit, a low-pass filtering circuit and an overvoltage and undervoltage protection circuit. By adoption of the low-pass filtering type voltage-stabilizing protection system, undervoltage and overvoltage protection can be carried out on an electric appliance load; when the mains supply power-supply voltage is instable to cause an undervoltage or overvoltage condition, a relay KA is released, namely, the load power supply can be cut off so as to protect the electric appliance load from being damaged under the undervoltage or overvoltage power supply condition; and therefore, the low-pass filtering type voltage-stabilizing protection system is suitable for popularization and application.