The　output　coupler　free　external　cavity　spectral　beam　combining　structure　uses　the　beam　along　0-order　and　1-order　diffraction　direction　as　the　feedback　light　beam　to　realize　the　wavelength　locking　of　the　emitters,　which　avoids　the　waste　of　0-order　and　1-order　diffracted　beams,　and　high　beam-combining　efficiency　can　be　obtained.　The　diffraction　efficiency　of　the　diffraction　grating　has　an　important　influence　on　the　beam-combining　structure＇s　feedback　efficiency　and　output　efficiency.　In　this　paper,　the　influences　of　grating　diffraction　efficiency　on　the　wavelength　locking　of　unpolarized　light　and　the　beam　combining　output　efficiency　are　simulated　and　analyzed,　and　the　stable　wavelength　locking　of　emitters　can　be　achieved　when　the　grating　diffraction　efficiency　is　78.9%-92%.　As　a　result,　the　highest　beam-combining　output　efficiency　can　be　achieved　by　using　this　external　cavity　spectral　beam　combining　structure　with　output　coupler　free.