The invention relates to an alarm for the approach of construction equipment to a high-voltage power transmission circuit, in particular to an alarm preventing large-size construction equipment such as cranes, and the like from approaching high-voltage power transmission circuits in a distance which is smaller than a safety distance. The alarm mainly comprises a detection device and an alarm device, wherein a circuit structure of the detection device comprises a transmission line distance sensing transducer, a safety distance judger, a transmission terminal frequency-modulation amplifier, a wireless signal generator and a transmission antenna which are all sequentially connected. A circuit structure of an alarm device comprises a receiving antenna, a wireless signal receiver, a second amplification dynatron, a frequency-modulation amplifier, a light emitting diode connected with the frequency-modulation amplifier, and a buzzer which are all sequentially connected. The invention can meet different requirements of the safety distance of transmission lines in different voltage levels, has convenient maintenance, can reduce the transmission line trip, casualties and equipment damage caused by the external damage of transmission lines by large-size construction equipment such as cranes, and the like, and can improve the power supply reliability of transmission lines.