The invention discloses a circuit for realizing AC input voltage limiting by means of a switch mode. The circuit comprises an input circuit module, a rectifier circuit module, a comparison circuit module, a field effect transistor drive circuit module, a switch circuit module and an output circuit module, wherein the input circuit module inputs the AC input voltage, and outputs the AC input voltage to the comparison circuit module after rectification of the rectifier circuit module, and then eventually outputs the AC input voltage through the output circuit module; the field effect transistor drive circuit module and the switch circuit module are connected to a power supply loop between the comparison circuit module and an output end line module; the comparison circuit module is provided with a voltage comparison function by means of setting of a voltage-regulator tube; a voltage signal being less than a voltage comparison threshold value can switch on a load power supply loop; and a voltage signal being greater than the voltage comparison threshold value enables the comparison circuit module to output a switch-on signal so as to drive on/off of MOS switch tubes which are connected with an original power supply loop in serial and to disconnect the power supply loop. The circuit for realizing AC input voltage limiting by means of a switch mode has the advantages of being small in volume, being high in efficiency, being low in caloric power, and being very low in cost.