The invention relates to an overvoltage sensor of overhead transmission lines, relating to an overvoltage monitoring device of the overhead transmission line of an AC power system. The sensor consistsof a voltage monitoring unit and a data acquisition unit, and is characterized in that the voltage monitoring unit mainly comprises an overhead transmission line, a sensing metal plate, a screening shell, a stainless steel screening box, a voltage-dividing capacitor, a front end protection circuit, a matched resistance, a coaxial-cable and the like. The sensor has the effects of simple structure,small volume, light weight, convenient installation, low cost, high safety, good universality, high linearity and high accuracy on testing overvoltage and the like. The invention can be widely used as the voltage sensor of the overhead transmission line, especially be applicable to overvoltage sensor of 10kV to 1000kV overhead transmission lines.