In the image type ballastless track subgrade settlement monitoring system, vibration and other factors are affected during the operation of the train. The relative deflection of the target surface and camera affects the accuracy of the spot center positioning results. Therefore, a monitoring target attitude measurement system is designed. The deflection angle is obtained by solving the target pose to achieve correction of the spot center positioning results. First of all, combine monocular vision with monitoring targets, establishing a perspective projection model of the camera according to a known geometric constraint relationship between the two-dimensional feature points of the target surface. Then, based on the P5P question, using the HOMO algorithm to solve the linear pose of the target surface linearly. On this basis, the pose optimization solution is obtained by the nonlinear Levenberg-Marqurdt algorithm. The system can perform real-time feature point image processing and pose calculation. An experimental platform for the target surface attitude measurement system in the surface settlement monitoring of ballastless track is constructed based on a high-precision three-dimensional precision rotary table, and mount the target surface vertically on the three-dimensional precision instrument. The data of the target pose measurement is obtained by controlling the rotation angle of the three-dimensional precision instrument. Experimental results show that when the X, Y, and Z axis are respectively rotated at [-5°, 5°],the root mean square error of the three directions of the pose measurement system is 0.048°, 0.052°, 0.056°, respectively. The entire measurement process time is 0.9 s. The time and accuracy of the measurement system meet the measurement requirements of the image-based ballastless roadbed surface settlement monitoring system.