In order to research the application of matter-element extension method in the evaluation of groundwater quality，the paper first introduced the method and then took the groundwater in a region of Beijing as research object.It conducted the comprehensive evaluation of water quality and detailed the evaluation standard of water quality, which made the evaluation result more accurate.The paper used the means of interrelatedness function and weighting factor method in order to exclude human intervention, made the result objectively reflect overall condition of groundwater quality. The evaluation accords with the local actual situation. The result indicated that the evaluation of region water resources situation by matter-element extension model is objective and tru.