Abstract: To verify the path planning in the laser tracking in-situ measuring process and to avoid fault operation, the simulation of the measuring process was realized. A 3D model of the measured gear was built based on the OpenGL graphics library. The models of the three-dimensional measuring platform and the laser tracker were built by using 3DSMAX and then they were imported into the simulation system.The touch detection between the probe and the measured gear was carried out using the Axis Aligned Bounding Box (AABB) method. The simulation system could communicate with the Renishaw's UCC2 controller, reading out the real-time coordinate value to update the status of the three-dimensional measuring platform model in the simulation system. Results show that the system ran stably, super-large gear measuring simulation and touch detection between the probe and the gear is realized.