The feasibility of realizing high efficiency spectral beam combining with multilayer dielectric (MLD) gratings based on conical diffraction was analyzed. The spectral beam combining approach was designed with the incident polar angle nearly equals to the Littrow angle based on the conical diffraction theory and two unit beams were experimentally combined. The experimental results indicate that, the diffraction efficiency nearly did not change in the case of conical diffraction when θ was constant and $ \varphi $＝6°. The combining efficiency of the output beam which was composited by two unit beams (wavelength equals to 1050.24 nm and 1064.33 nm respectively) with incident polar angle θ of 43.99° was 92.9%, 8.8% higher than that of approach based on non-conical diffraction. The beam quality factor after combining were M_x²＝1.204 and M_y²＝1.467, which were almost equivalent to that of approach based on non-conical diffraction.