Both the digital library and the digital reference service were invented and have been developed under the networked environment. Among their intersections, the fundamental thing is their symbiotic interest--serving the user in a more efficient way. The article starts by discussing the digital library and its service and the digital reference service and its collection. Then, based on a series of case studies, the article explores the necessity of their three-dimensional integration, i.e. the completely parallel integration, the digital reference service affiliated with a digital library and a digital library integrated into the reference service. It is proposed that the two communities could achieve improvement simultaneously through mutual complementarity. (Contains 5 figures and 1 note.)