Abstract: We have achieved 856 W spectral beam combining output of two fiber lasers employing a transmitting volume Bragg grating (TVBG), which is the highest combining power of spectral beam combination by VBGs. The total spectral combining efficiency is 73.7% and the beam quality of combining beam is 7.9 and 2.7 in x and y direction, respectively. Though the diffraction beam is seriously stretched by angular dispersion of TVBG, the transmission beam preserves its beam properties in the high average power spectral beam combining. This indicates that the broadband fiber lasers (the spectral bandwidth is over 4 nm) can be used as transmission beam in high efficiency spectral beam combination of VBGs for higher combining power output.