To realize the large-scale and high-precision displacement measurement, a new method based on a virtual detector was described according to the basic principles of traditional laser triangulation method. The CCD subsection measurement was used to enlarge the measuring range and to implement the displacement measurement. Three independent CCDs were distributed uniformly along the optical axis and a plain reflected mirror was regarded as the virtual detector.When the beam image was reflected by the plane mirror, the beam was imaged by CCDs. The designed system is equivalent to that a CCD is added, therefore, the measuring range is enlarged. Furthermore,the collimator filter is composed of a collimation system, a polarizer and a diaphragm. It shortens the diameter of the image spots on the photosensitive surface of the detector,and reduces the influent of unideal optical spots on the measured surface on the measuring accuracy.The high-precision measurement of large displacement is achieved. The results are in agreement with the experimental observation.