The study on detecting the trajectory of planar controllable linkage mechanism based on computer vision was presented. Firstly, a visual detection system with camera as the basic part was formed, and the problem of data lost in the process of image acquiring has been solved. The sequence image of object was acquired by the calibrated camera system, and the trajectory of object was gained by the algorithms of image processing, object detection and location. The visual detection method for planar controllable mechanism has been realized, and the result is satisfactory.