We have studied the Ge(112)-(4×1)-In reconstruction with scanning tunneling microscopy (STM). Based on our bias dependent STM images and the characteristic electronic structure of stable submonolayer group Ⅲ-metal/group-Ⅳ-semiconductor interfaces, we propose an atomic model of this reconstruction for further investigation. The adsorption sites of In atoms are the same as In atoms' adsorption sites in the Si(112)-(7×1)-In reconstruction, but are different from the adsorption sites of Al and Ga atoms on the Si(112) surface. We suggest that this difference in adsorption sites is mainly due to the longer covalent bond length of In atoms. We further propose that, due to the smaller misfit, Al and Ga atoms may form longer nano wires along the step edges on the Ge(112) surface.