The invention discloses a motion precision testing device for numerical control devices, which comprises a signal conditioning plate connected with a numerical control device, a data collecting card and a programmable computer, wherein level conversion or input-output conversion of pulse signals or feedback signals which are real-time received and outputted by the numerical control device can becarried out by the signal conditioning plate, the data collecting card receives signals input by the signal conditioning plate at real time to convert the signals into computer readable signals and outputs control signals to the numerical control device, and the programmable computer equipped with a storage module stores processing procedures or operating parameters of the numerical control device and then builds up the theoretical trace, controls the data collecting card to output control signals, reads pulse signals or feedback signals of the numerical control device which are inputted by the data collecting card, builds up the real-time operating trace, and displays the theoretical trace and the real-time trace to output. The invention constructs a software and hardware platform according to motion characteristics of the numerical control device, and tests the motion characteristics of the numerical control device via simulated operation, which has high efficiency, simple operationwith various testable contents, wide application scope and high testing precision.