Abstract: To improve the machining accuracy of five-axis NC machine tools,this paper analyzes the RTCP errors of five-axis machine tools with dual head.The error analysis model is established based on the basic theory of a multi-body system and six-degrees of freedom of the rigid body.RTCP errors of tool center point and tool vector are deeply analyzed.The error formulas of tool center point and tool vector are deduced.By comparing the ideal and actual cutter path that are generated by tool path simulation software,the model is demonstrated to be correct.The study provides fundamental theory for error compensation and error analysis.