A single high-power fiber laser has limited output power and cannot meet higher requirements in the latest applications of industry and national defense. To achieve higher laser power output, a fiber laser spectral beam combining(SBC) scheme that ensures beam quality at high-power is proposed. This scheme combines transmission gratings and reflection gratings, and constructs a three-dimensional non coplanar optical path compression structure through a multi degree of freedom reflection mirror group, significantly improving the compactness and optical path density of the system, optimizing the interference light influence and thermal stability issues in the spectral beam group. Replace aluminum-based composite materials with invar material as the optical component structure, and use optical epoxy adhesive instead of RTV silicone rubber to connect the reflector, matching the coefficient of linear expansion between materials. The beam combining system reduces the spot degradation caused by thermal conduction during high-power output, and continuously outputs high-power lasers with beam quality M2less than 2, which proves the stability and efficiency of the beam combining system proposed in this scheme.