Disclosed is an apparatus and method for ray-tracing using a path preprocess. The method for ray-tracing including launching a ray from a transmitting point at angles with regular intervals, setting a first side of an object where the launched ray is projected as a reference patch, and searching predetermined preprocessed path data for a counterpart patch corresponding to a second side of another object, the second side being exposed to the projected ray reflected or diffracted from the set reference patch, and tracing a transmission path of the reflected or diffracted ray.