The vertical measurement method is simple and effective to observe the displacement of dam deformation, which has been widely used in the actual dam deformation monitoring. To solve the problem that most of the existing pendulum telecoordinometer can only measure the two-dimensional displacement of the pendulum line and the structure is complex, a 3D pendulum line measurement method based on linear structured light is proposed in this article. Based on the fact that pendulum line direction keep constant, this article uses the principle of linear structured light measurement to achieve pendulum line three-dimensional displacement measurement. Firstly, the two-dimensional displacement of the pendulum line is obtained by the linear structured light measurement. Then, based on the fact that the imaging light of the fixed mark points on the pendulum line intersects the pendulum line at one point, the threedimensional displacement measurement of the pendulum line is realized by synthesizing the two-dimensional measurement results of the pendulum line and the imaging light equation of the fixed mark points recovered by the camera internal parameters. The experimental results show that the displacement measurement accuracy of this method is ± 0. 1 mm in the Y direction of the horizontal plane, and ±0. 05 mm in the X direction and Z direction of the horizontal plane, and the measuring range is 0~ 80 mm. Compared with the current vertical displacement measurement method, the vertical displacement measurement accuracy and measuring range are higher, and the measurement structure is simpler.