The　fracture　debonding　failure　of　cement　plug/casing　interface　caused　by　the　migration　of　underground　fluid　with　pressure　accumulation　imposed　serious　challenges　to　wellbore　integrity　of　abandoned　wells.　This　paper　presents　an　investigation　with　a　view　of　quantifying　the　relationships　between　the　fracture　debonding　height　and　the　migration　time　of　underground　fluid.　A　new　3D　numerical　model　of　cement　plug/casing/cement　sheath/formation　system　based　on　the　cohesive　zone　method,　which　was　validated　by　microannulus　experiment,　was　developed　to　simulate　the　fracture　debonding　process.　And　then　the　relationships　between　fracture　debonding　height　and　propagation　pressure　was　studied.　Additionally,　the　influence　of　horizontal　in-situ　stress,　cement　plug　mechanical　parameters,　and　interface　properties　on　the　fracture　debonding　height　and　development　geometry　were　also　analyzed.　The　results　of　research　indicated　that　the　minimum　horizontal　in-situ　stress　played　a　decisive　role　in　controlling　the　fracture　propagation　of　cement/casing　interface.　Debonding　fracture　propagated　along　the　whole　circumference　of　the　interface　with　the　same　height　for　the　case　that　the　horizontal　in-situ　stress　was　uniform,　while　propagated　along　a　certain　circumference　angle　of　the　interface　with　the　maximum　height　in　the　direction　of　maximum　horizontal　principal　stress　for　the　case　that　the　horizontal　in-situ　stress　was　non-uniform.　The　results　of　numerical　analysis　showed　that　lower　elastic　modulus　and　Poisson＇s　ratio　of　cement　plug,　higher　cement　plug　permeability,　and　larger　critical　normal　strength　and　critical　shear　strength　were　beneficial　to　decrease　the　fracture　debonding　height　and　reduce　the　risk　of　debonding　failure　of　the　cement　plug/casing　interface.　Finally,　some　effective　measures　to　maintain　the　sealing　integrity　of　abandoned　wells　were　proposed.