The protection of the ecological environment of lower Tarim River valley is an important objective in the integrated harnessing of the Tarim River. The lower Tarim River valley is characterized by sparse population, arid climate and bad natural environment, and hence it is especially important to work out an easy and rapid method for detecting the underground water table of this area. This paper reports the results of applying SWS-3 type engineering exploration and exploration detection instrument to detecting the underground water table of lower Tarim River valley, and describes in brief the variation regularity of the phreatic water table in lower Tarim River valley.