Abstract: Excavation of urban underground geotechnical engineering has become an important research topic because of its effluence on the safety of environment. This paper presents in details description about the underground tunnel project of the Middle section of the South-North Water Diversion located at Beijing west-fourth ring.Generally speaking,the contents can be stated as follows: potential serious effects and key controlling factors that are resulted from complicated projects and geological environment;primary support methods and construction controlling and monitoring measures in order to obtain effective control and minimize the effects;analyses and examinations for the monitoring controlled results.The practice shows that even if under complicated project environment,the effects resulted from underground geotechnical engineering excavation can get effective controlling.