The invention discloses an X-ray-based overhead wire field detecting device and detecting method. The device comprises a main frame, a frame fixation bracket and a controller. The main frame is connected with an imaging plate embedded component and an X-ray machine embedded component. The controller is connected with an X-ray machine and a sliding member. The frame fixation bracket enables the whole device to be fixed on an overhead wire. The imaging plate embedded component and the X-ray machine embedded component are controlled to slide along the main frame by the controller, thereby adjusting distances among an imaging plate, an X-ray machine, and a to-be-detected overhead wire; and thus the X-ray machine can carry out focusing relative to an adjusting forming plate. After the distancesof the three parts are adjusted to be at focusing positions, the X-ray machine carries out transmission and imaging to obtain an image being able to reflect the overhead wire condition well, so thatdefect detection can be carried out on the overhead wire or wire clamp effectively. The detection process becomes simple and the detection efficiency can be improved obviously.