Abstract: The micro-compound turn-milling machine tool can complete most parts processing processes in one clamping process. It is an indispensable CNC equipment for processing micro complex structural parts. As a precision machining CNC equipment, its own spatial geometric error directly affects the machining accuracy of parts. The ultra-precision micro-compound turn-milling machine tool CXKG25-I developed by Beijing Institute of Technology was used as the research object in this paper. First, the spatial geometric error elements of the ultra-precision turn-milling compound machine tool were analyzed, and the 57 spatial geometric errors were obtained. The spatial geometric error model was established based on the multi-body system theory method. Then, the sensitivity analysis of the spatial geometric error project was carried out, and the key sensitive factors of machining errors were revealed. These analysis results guide and optimize the structural design and manufacturing of ultra-precision turn-milling machine tool.