Research conclusions: (1) The Line 3 of the urban rail transit in Kunming crosses the Kunming downtown featured with the complicated and unfavorable engineering geological condition and hydrogeological condition，such as the multiple rock － soil layers，rich underground water，sandy soil liquefaction，karst，shallow natural gas，filling soil，soft soil，the special rock and soil and poor regional stability．(2) Based on the comprehensive analysis of the geological condition and surrounding environment of deep foundation pits，the open cut method was used for the foundation pit and the top－down method was used for the section where was limited locally by the transportation condition．(3) The diaphragm wall was available for the interior support and sealing up for the deep foundation pit in the basin with the support of the concrete and steel pipe． The drainage ditch and the collecting well were installed in the foundation pit along with the artificial pumping and draining． The mixing pile and filling were used for the pit base to meet the requirement of anti－float and anti－raising．(4) The the slope excavation could be conducted with the support of the soil nail wall and filling to the pit base for the foundation pit in the essentially level area because of its good engineering geological condition without development of underground water．