The present invention relates to a combined retaining wall structure; a certain concrete casting space is arranged between a front retaining wall precast block and a back retaining wall precast block; at least one vertical fixed structure piece is arranged on any one side of the two sides of the front retaining wall precast block and the back retaining wall precast block by a first fixing pin; atleast more than one space fixing structure piece is arranged on any one side of the surface and opposite surface of the front retaining wall precast block and the back retaining wall precast block invertical state by a second fixing pin; on the basic concrete structure piece, the combined front retaining wall precast block and the back retaining wall precast block are laminated in multistage according to the needed height; after binding the space fixing structure piece and the vertical and level reinforcing steel bars by a binding structure piece, the concrete casting space can cast the concrete. The structure does not need to manufacture moulds for casting the concrete of the basic concrete structure piece. The structure has the advantages of shortening completion period, reducing laborand labor cost, and capable of finishing various patterns and designs in advance on the front retaining wall precast block.