The invention provides a beam combiner, a beam combiner monitoring system, and a monitoring method of the beam combiner monitoring system. The beam combiner includes an outer sealing box, a pluralityof fibers and a free fiber, wherein the plurality of fibers are pulled into a cone-shape to form a cone region; a fiber grating region is arranged on the free fiber; the plurality of fibers, the coneregion, the free fiber and the fiber grating are arranged in the outer sealing box; or the fiber grating region is arranged on one free fiber. The invention also includes a monitoring system with thebeam combiner and a monitoring method thereof. By setting the fiber grating region on the fiber while the fiber grating region is located in the outer sealing box, the corresponding wavelength changecan be obtained through the fiber grating region, and the change of the corresponding stress or temperature can be obtained by means of a wavelength variance, so that real-time monitoring of the stateof the beam combiner can be realized.