Abstract: In order to realize in-orbit measurement of the parameters of three-line array satellite-borne CCD camera, a method for measuring 6-DOF (Degree of Freedom) micro-displacement was proposed in this paper. The LED output light with high brightness was collimated and coupled to the input optical fiber. The end of the output fiber was fixed to the movable object to be measured. The fiber outputs were collimated by multiple fiber collimators ( 4) and captured by multiple area array CCD cameras ( 4) in the fixed part of the system. The 6-DOF displacement of the measured object was solved according to the position change of the light spot in the CCD image. In order to validate the model of the system and 6-DOF displacement calculation program, the proposed method was theoretically analyzed and simulated. The results show that both the maximum translational error and rotational error of the typical 4-collimation measurement system are under 10-5 m and 10-4' when the translational displacement is less than 100 m and the rotational displacement is less than 6'. And the limit errors (3) of the translational errors and rotational errors are respectively 0.9 m and 0.012' when the random quantities of -0.5-0.5 m are added to the two coordinate directions of the position of the light spot of the collimators.