The invention relates to a turning radius detecting device, system and method for a high-voltage single-core cable. The device comprises a body. Rollers are arranged at the bottom of the body. The body can move along a cable to be detected through the rollers. A button unit is arranged on one side wall of the body. A gyroscope, an ultrasonic transceiver, a main control unit and a wireless transceiver are arranged in the body. A display unit is arranged on the surface of one side of the body. The button unit, the gyroscope, the ultrasonic transceiver, the wireless transceiver and the display unit are electrically connected with the main control unit respectively. According to the invention, the device can conveniently move on the cable to be detected through the rollers; different turning radius detecting devices can be set in the same plane through the gyroscope; the ultrasonic transceiver carries out ultrasonic ranging to accurately measure the turning radius of the detected cable; deviation caused by the experience of manual construction personnel is avoided; the measurement precision is high; and the whole device is small in volume, is particularly suitable for cable laying construction in an underground small space, and is convenient to carry.