An optical fiber grating tracker includes a first stub, a second stub, an optical fiber grating, and a connection part. The connection part has a through hole. The first stub is inserted into one end of the through hole. The second stub is inserted into the other end of the through hole. An interval exists between the first stub and the second stub. The optical fiber grating is in the through hole and in the interval. A space in the through hole is filled with a waterproof material. The optical fiber grating tracker and the method for detecting an optical fiber line fault can detect an optical fiber fault from an optical fiber truck to the optical fiber grating tracker through an optical splitter, and meanwhile do not affect normal communication of an original optical communication network.