1. A system for determining coordinates in a three-dimensional space using a beam phase interference method, comprising: a light source for providing beam to two optical fibers, one end of each of the two optical fibers being set inside a probe, the probe being placed in the three-dimensional space; a fiber coupler placed in front of the light source, the fiber coupler splitting beam emitted from the light source into two beams, the other ends of the two optical fibers being connected to the fiber coupler, one of the two optical fibers being connected with a PZT for changing an optical path; an image capturing unit for acquiring an interference pattern generated by beams emitted from the two optical fibers set inside the probe; and a control/analysis unit for calculating the acquired interference pattern to determine curvature and central point of the interference pattern.