Accurate laser positioning system (ALPS) is widely used in large space indoor dynamic positioning. To improve the positioning accuracy and refresh frequency, the inertial measurement unit (IMU) with a high frame rate is used for fusion, so it is necessary to calibrate the external parameters of ALPS and IMU. Based on the analysis of the calculation process and error description of traditional calibration, we propose a calibration method of spatial multipose transformation (SMT). In this calibration method, the target plate performs multiple attitude transformations to obtain the attitude data and process its error. Then, the Lodrigues matrix is introduced in the solution process to reduce the dimension of unknown variables in the equation, and it is optimized combined with SVD decomposition. At the same time, to further adapt to the application of fusion, a more intuitive error description method is proposed to evaluate the influence of calibration results on fusion accuracy. The simulation experiments indicate that the proposed method enables the calibration error to have accuracy within 0.02 mm. Furthermore, the results of the validation experiments show that the proposed calibration solution method improves in accuracy and robustness with respect to the conventional method. It provides a technical basis for realizing higher precision indoor dynamic positioning applications in large space.