The hydrogen-adsorbed diamond (001) surface is studied by ab initio pseudopotential method. The bare and monohydride surface configurations are calculated.The alteration of the charge density redistribution of the monohydride surface shows the formation of the C—H bonding, which leads to electron transfer from carbon atoms in the surface layer to the absorbed H atoms. The mechanism of alteration for charge density redistribution is discussed, which provides a theoretical background for the previous experimental observations and the model of electrical properties of diamond surface.