Aiming at the problem that the target deviation of settlement monitoring system affected the accuracy of settlement monitoring, a monitoring target attitude measurement system was designed to realize the real-time non-contact measurement of target pose. Firstly, the monocular vision and the monitoring target surface were combined, and the perspective projection model of the camera was established according to the known geometric constraint relationship between the two-dimensional feature points of the target surface. Then, for the five feature points arranged in a cross, based on the PnP problem, the HOMO algorithm was used to linearly solve the target pose. Based on this, the pose optimization solution was obtained by the nonlinear L-M algorithm. The system could perform real-time feature point image processing and pose calculation. An experimental platform for simulating the target pose measurement system in the surface settlement monitoring of ballastless track was built. The experimental results showed that the root mean square error of the three angles of the pose measurement system is 0.126°, 0.14°, 0.12°, and the whole identification process takes 1.9s. The measuring system had high calculation accuracy and was used in a short time, which was suitable for the flawless track surface settlement monitoring system.