The invention relates to an undercarriage safety monitoring method based on course line and visible data fusion. The method comprises the steps of providing an image monitoring module arranged at an airfield runway and a main control system arranged in a main control room and matched with the image monitoring module; searching, by the image monitoring module, a target aircraft on four sides of a rectangular traffic pattern, and when the target aircraft appears on four sides to five sides of the rectangular traffic pattern, i.e., appears a target aircraft undercarriage place, performing, by the image monitoring module, automatic target detection on the target aircraft, tracking and analyzing the target aircraft via the main control system, judging whether the target aircraft undercarriage is laid down, and then providing an early warning signal. The method greatly facilitates acquisition and analysis on the state of the aircraft undercarriage in the flight process, can judge the flight state of the aircraft, and provides technical and data support for planning of the course line and the laying-down strategy of the aircraft undercarriage.