The present invention demonstrates a solid fuel grade gasification-combustion dual bed poly-generation system, comprising a combustion system, a gasification system, a synthesized gas cooling and purifying system and a synthesized gas methanation system. The combustion system is connected with the gasification system through a circulating material return system. The gasification system mainly adapts the circulating fluidized-bed combustion mode. The gasification system adapts the fluidized-bed incomplete gasification method and the generated semi-coke is returned to the combustion system for re-utilization. The synthesized gas purifying and cooling unit adapts water cycling and combustible recycling. The by-products, CO2 and steam, in the methanation unit can be recovered, so the maximum utilization rate of energy in this system is realized.