Abstract : Rotational errors occur when a spindle rotates. This testing system, built using LabVIEW virtual instruments, can be applied to the measurement of various spindle rotational errors. This paper introduces the concept, generation, and measurement significance of rotational errors, and presents the measurement principle of three-point centering. The system composition and testing process are described, and the measurement error of the system is analyzed, calculating the influence of installation errors on the measured values. The hardware used in the system is a virtual instrument, and its function is explained. The software is LabVIEW, and its testing program is also provided. Keywords : spindle; rotational error; testing system; LabVIEW; virtual instrument 0. Introduction The rotational accuracy of a machine tool spindle is one of the important aspects of machine tool geometric accuracy. The International Institute for Production Engineering (CIRP) has clearly defined the spindle rotation axis as follows: the rotation axis is a line segment around which a specified object rotates, this line segment is fixed to the rotating body, and together with it moves axially, radially, and angularly relative to another line segment called the axis mean line. The line segment of the average axis is a line segment fixed on a non-rotating object and located at the average position of the axis of rotation. When the spindle rotates, there must exist an axis of rotation (here, we assume the spindle is a rigid body). Theoretically, we hope that the position of this axis in space remains stable, i.e., an ideal axis. However, in actual operation, the axis of rotation changes every moment. The trajectory of the axis of rotation in space is called the spindle rotation error. Factors causing spindle rotation error include: spindle bearing clearance, lubrication conditions, and structural factors and dynamic characteristics such as vibration during operation. Since the spindle rotation error directly affects the machining accuracy of the workpiece, real-time processing of the measured error data to obtain accurate and quantitative evaluation is of great engineering significance. This test system analyzes the influence of installation error on the calculation results based on the system structure and working process. After theoretical analysis and experimental verification, its test method is feasible, realizing the measurement and real-time analysis and processing of spindle rotation error. [Full text download of the virtual instrument-based spindle rotation error test system]