A novel spatial position measurement technique for an optical fiber based on diffraction phenomena is demonstrated. This technique enables in-situ measurement of the spatial position of a fiber. The diffraction pattern of a fiber undergoes a change in its intensity and shape as the spatial position of fiber deviates from reference axis. In this study, theoretical and numerical analysis, a description of technique and its simulation result are presented as well as experimental setup and result for verification of feasibility of this technique. Expected application areas are also outlined in the future works section.