For　pit-in-pit　excavated　in　the　bottom　of　outer　pit,　the　failure　mechanism　of　basal　heave　is　more　complicated　than　normal　pit.　Finite　element　method　based　on　the　reduced　shear　strength　technique　is　used　to　evaluate　the　basal　heave　stability　of　pit-in-pit　excavations.　The　influence　of　spacing　between　inner　and　outer　pit,　width　and　depth　of　inner　pit,　depth　of　inner　and　outer　wall　insertion,　undrained　shear　strength　of　clay　on　the　failure　modes　and　factor　of　safety　is　analyzed.　In　conclusion,　there　are　three　kinds　of　failure　modes　of　pit-in-pit　excavation:　entire　failure　of　inner　and　outer　pit　(M1),　entire　failure　of　inner　and　outer　pit　(M2),　failure　of　outer　braced　pit　(M3).　The　critical　value　of　parameters　is　determined　for　the　change　of　different　failure　modes.　The　basal　stability　of　pit-in-pit　excavations　will　increase　with　the　spacing　between　inner　and　outer　pit,　The　depth　of　inner　and　outer　wall　insertion,　and　the　undrained　shear　strength　of　clay.　Nevertheless　it　will　decrease　with　the　increase　of　width　and　depth　of　inner　pit.　©　2020,　Editorial　Office　of　Journal　of　Xi＇an　University　of　Architecture　&　Technology.　All　right　reserved.