Abstract: For the feed system of CNC machine tools with dual-position closed-loop feedback, the backlash in its transmission accuracy directly affects the machining accuracy and quality of workpieces. In this study, a high-efficiency, high-precision, and on-line implementable backlash detection method for the feed system was developed by utilizing the closed-loop linear scale system equipped on the machine tool itself. The experimental results demonstrate that the maximum deviation between the backlash detection accuracy of this method and the laser test data is within 0.2 μm, and it can be realized by running a short-duration test program. Meanwhile, this study provides a theoretical basis and technical support for the dynamic accuracy compensation of CNC machine tools and the health status evaluation of ball screws.