Abstract: The measuring instrument was developed on the latest software platform LabWindows/CVI supplied by an American company, i.e., the National Instruments, with the data acquisition card and existing lab apparatus used as hardware platform. The virtual measuring instrument combines the technology to measure the form position error with virtual instrument to evaluate the axis straightness error by least square method and minimum zone estimation. Then, the image of axis straightness error is able to display on screen visually, thus analyzing the cause of axis straightness error. The measuring instrument has the advantages of high accuracy, reliable and stable operation and low cost, especially the excellent function expandability. It is available to lab teaching and industrial applications.