The invention discloses an automatic detection system and automatic detection method of a cable erection height, and relates to the technical field of cable height measurement, for accurately measuring the relative height of a cable at a natural sagging state. The automatic detection system of the cable erection height is characterized by comprising a contactor, a support rod, a stay wire, a detector and a laser reflection plate, wherein the contactor comprises a carriage, an upper platform plate, a middle platform plate and a lower platform plate, the upper platform plate and the lower platform plate are respectively slidably connected with the carriage along a vertical direction, the middle platform plate is fixedly connected with the carriage, the upper side surface of the upper platform plate is provided with a roller frame, the roller frame is rotationally connected with a roller, the axis of the roller is parallel to the upper platform plate, the lower side surface of the upper platform plate is fixedly connected with a pressure rod, and the upper surface of the middle platform plate is provided with a pressure transducer. The system has the advantage of accurately measuring the height of the cable at the natural sagging state.