The invention provides an undersized log light wood structure composite shear wall, and belongs to the technical field of shear walls. The undersized log light wood structure composite shear wall comprises undersized log composite studs, a wood-based structural board, top beam boards, a bottom beam board and a gypsum board. The undersized log composite studs are vertically arranged, each two adjacent undersized log composite studs are parallel to each other, the upper end of each undersized log composite stud is fixed on the top beam boards, the lower end of each undersized log composite stud is fixed on the bottom beam board, the undersized log composite studs, the top beam boards and the bottom beam board form a wall formwork, the wood-based structural board is fixed on one side of the wall formwork, and the gypsum board is fixed on the other side of the wood-based structural board. Undersized logs are applied in the light wood structure, and the undersized log composite studs substitute for most of dimension stock studs, so that consumption of dimension stocks is reduced, domestic undersized log resources can be utilized fully, cost of the light wood structure can be lowered, and application of the light wood structure in China and particularly in modern rural buildings is benefitted.