A new method of aiming and positioning the measured points of a large workplace by a laser beam and measuring the large distance accurately by a dual frequency laser interfe-rometer are presented in this paper. In this way ’the distance between centers of two quadrant silicon, hotodlades on the chucks can be mea-sured by a dual frequency laser interferometer. The dimension of the measured diameter can be calculated by a simple equation. The experiment results show that the relative measurement error is less than 5×10-6.