Abstract: It was named as Sanjiang(which mean Nu River,Lancang River and Jinsha River in English)Sector on YunnanTibet railway east from Lijiang city in Yunnan province and west to Basu county in Tibet Autonomous region,and it was conformed the Sanjiang sector was the most difficult sector on railway construction,especially there exited complex engineering geological problems.By the authors recent-year study,some new understandings on fundamental geology were put forward,thus recognitions on the possible railway engineering geological problems were fundamentally rooted out.The strata or rock distributed extensively in Sanjiang region were Paleozoic limestone like islands surrounded by Mesozoic sandy mudstone,and then the late Yanshan period magmatite was developed there.The connection between earthquake and active fault was not very close,and there were no obvious regional fault signs.It was comprehensively realized there existed many deep-level railway engineering geological problems in Sanjiang sector including the problem caused by karstification in limestone areas,the problem caused by soluble salts precipitation in clastic rocks areas,the problem in drop-style slide rockmasses,the problem caused by earthquake,the problem in high geothermal temperature areas and the problem caused by cleavable zone.Each type of the problems were corelated.The sub sectors with serious problems were the sector from Lashi lake in Yulong county to Hutiao town street in Sangrila county,Baima Snow Mountain sector in Deqin county,Meili Snow Mountain sector in Deqin county and Lengqu sector in Basu county,which should be deeply researched and treated by countermeasures.