Abstract: The precision measuring instruments for large-size objects are widely used in recent years; their accuracy is affected by environment, instruments, operation, and many other factors. This paper presents a measuring approach of Unified Spatial Metrology Network (USMN) for large-size objects. This method can integrate all instruments involved in the measurement process, and the measurement uncertainty can be jointly dealt with to optimize measurement results. Through the laser tracker switching, multiple measurements of the coordinates of measured points in space are made, and the uncertainty of the measurement system is analyzed. Experiment results show that the USMN can combine all the stations of the measurement results, and the synthetic precision is superior to each local precision.