Calibration is an essential work in three-dimensional scanning system. The operation of existing calibration is complex and tedious. In this paper, we design a DLT-based automatic method of calibration, in which the calibration reference points are detected automatically. Then we can figure out a series of calibration parameters from these points. The average value of all parameters is just the calibration parameters. The experimental results show that the method we proposed is not only guaranteeing the calibration precision but also simplifying the calibration operation comparing with the traditional manual calibration method.