After the parameter calibration of a projector, it can be considered another camera and combined with a binocular system to form a trinocular stereo vision system. In contrast to the traditional calibration method using high-precision plane targets, the proposed method only needs a simple and unmarked white paper target to obtain the world coordinates of the characteristic points provided by a binocular system. The linear model and distortion correction model containing the distortion coefficient of a thin prism are used to complete the preliminary parameter calibration of a projector, and an improved beam adjustment method is used to estimate the global optimal parameters of the projector and a dual camera. Results of calibration verification experiments show that the proposed improved beam-adjustment method can achieve parameter optimization. A measurement comparison experiment on a standard plane showed that the resulting trinocular stereo vision system could enhance measurement accuracy.