In order to overcome the difficulties in the real-time measurement of plane angle in many fields such as manufacture and architecture,a non-contact measurement method is proposed based on machine vision. In the method,first,a circle and its center are marked in each of two planes to be measured,and only one digital camera with known intrinsic parameters is needed to take photos once in any position so as to obtain one image with the centers and all or part of the circles. Then,the equations of the images of the circles and the coordinates of their centers are acquired by means of the least square method,thus achieving the equations of the vanishing lines in the two planes and the coordinates of the vanishing points in the normal directions of the two planes. Finally,according to the imaging equation of the camera,the angle between the normals of the two planes,whose supplementary angle is just the angel between the two planes,is figured out by using the coordinates of the vanishing points and the intrinsic parameters of the camera. Experimental results show that the proposed method is simple and feasible,with a relative measurement error of less than 1%,which can meet practical requirements satisfactorily.