A gate detection robot based on a giant magnetoresistance element includes a support, a guide wheel, and two driving wheels are provided at the bottom of the support. The support is provided with a controller, a range-based localization module, and a magnetic flaw detection sensor based on the giant magnetoresistance element. The magnetic flaw detection sensor includes an excitation mechanism, a giant magnetic sensor, and two magnetic concentrators. During detection, the excitation mechanism magnetizes a gate with a magnetic field as a medium. When the surface of the gate has a defect, the magnetic conductivity of the local area is reduced and the magnetic resistance is increased so that magnetic lines are distorted and diffused outside the gate to form a detectable leakage magnetic field signal, the signal is transmitted to the controller, so that the controller obtains a specific location of the detection robot.