Precision measurement technologies have been developed for a long time. Measuring the displacement of meso-scale objects became an important issue in the recent years. In this study, a displacement measurement system for meso-scale objects is developed by combining the measurement technique of using position sensing detectors (PSD) and the grinding skill of fabricating micro scale reflection surfaces on optical fiber tips. This measurement system can be used for detecting the postweld shift (PWS) of a laser-welded butterfly-type laser diode module package. The PWS affects the coupling efficiency of a laser-welded butterfly-type laser diode module package quite a lot. Although there are many papers studied the measurement of PWS, most of the measurements are less than 6 degrees of freedom (DOF). The system developed in this paper can measure the 6 DOF displacement of the PWS. An attachment for carrying 3 micro reflection probes is designed firstly which will be settled on the fiber ferrule of a laser diode module. After all the coordinate transformation matrices of the laser beam light source, micro reflection surfaces, and the position sensing detectors are derived as well as the PSD readings are taken, displacements of the ferrule of a laser diode module can be solved from the displacement equations by using numerical method. The system developed in this paper is implemented on a Newport butterfly-type laser diode module package station (Model LW4200) for demonstration. The testing results show that the resolution of this system is 1£gm and the accuracy is 2£gm. Beside the application of measuring the 6 degrees of freedom PWS of a laser diode module package, the system developed in this paper can also be applied for measurement the displacement of other meso-scale objects.