An amplitude control main circuit, a voltage supply modular circuit, a display device, and an amplitude control method are provided. The amplitude control main circuit includes a variable resistive circuit, an output control circuit and a gate-driving-power-voltage output terminal; the output control circuit is connected to an output control terminal, a voltage input terminal, the gate-driving-power-voltage output terminal, and the variable resistive circuit, and controls, under control of the output control terminal, the gate-driving-power-voltage output terminal to be connected to the voltage input terminal directly or via the variable resistive circuit; a control terminal, a first terminal, and a second terminal of the variable resistive circuit are connected to a resistance control terminal, the output control circuit, and the gate-driving-power-voltage output terminal, respectively, and a resistance value of the variable resistive circuit is changed under control of the resistance control terminal.