Taking the HJ044 dual rotary table fiveaxis numercial control (NC) machine tool as an example, using the builtin sensor information of machine tool and the theory of multibody system as basis, and built kinematics modeling of tools related to parts, a dynamic machining error online monitoring method of NC machine tool based on buildin sensors was put forward. The method was directly used of the machine tool encoders or grating ruler of builtin sensor for information acquisition such as machine tool all axis motion displacement, and combined with kinematics model of the machine to measure machining error induced by dynamic charaateristics of the machine tool. The experiment shows that this method is an effective and simple dynamic machinining error onling monitoring and measuring method of NC machine tool.