Disclosed is an operational amplifier based on a metal-oxide TFT. The operational amplifier includes an auxiliary amplifier and a bootstrap gain-increasing amplifier. The auxiliary amplifier adopts a two-stage positive feedback structure, including a fifth transistor, a seventh transistor, an eleventh transistor, a first amplifying unit, and a second amplifying unit. A gate of the fifth transistor serves as an input end of the operational amplifier. The bootstrap gain-increasing amplifier includes two second circuits in mutual symmetry. Each of the second circuits includes a first transistor, a second transistor, and a current source unit with a bootstrap structure.