1. A method for retrieving a similar sentence to a source sentence inputted by a user through a translation memory in a translation aid system, comprising the steps of: (a) constituting an inverted file of an index word and a translation memory from a parallel corpus; (b) filtering candidate sentences having a high similarity by comparing the source sentence provided by the user with sentences of the constituted translation memory; and (c) outputting a source sentence and a corresponding target sentence in the order of similarity by calculating similarity between the filtered candidate sentences and the input source sentence.