The invention discloses a system for detecting a power transmission line object. The system comprises a camera, wherein the camera is connected with a video server through RS485; a video output by the video server is sent into an image acquisition board; the image acquisition board is connected with an upper computer; the upper computer is connected with a base station and an alarm device; the image acquisition board is also connected with a DSP (digital signal processor) high-speed compression circuit and a storage and uploads a control command sent by the upper computer to the video server; the video server controls the camera to take photos; an image shot by the camera is uploaded to the image acquisition board through the video server; and the image in the image acquisition board is compressed by the DSP high-speed compression circuit and is matched with a standard image in the storage. The invention also discloses an object detecting method. An invasion and a foreign object can be detected by the system and the method, and if an abnormal object is found, alarm is performed, so that a worker takes an effective measure to avoid accidents of a power transmission line and uploads the alarm information by level by one level.