Abstract: The waste dump of Tibet Jiama Copper Mine, which has a steep and soft base, is taken as the engineering background to reveal the failure mode and mechanism with assistance of similarity simulation principle.Using a method combining bottom friction test and numerical simulation.The deformation evolution of the waste dump is obtained by the contactless displacement monitoring system.The experimental results show that: ①The deformation and instability of the soft steep base dump can be divided into three stages: unloading deformation at the slope toe, vertical tensile crack penetration and tensile crack propagation.②The soft soil layer at the base is compressed and the soft soil layer at the slope toe is subjected to shearing.The slope toe is the trigger zone for slipping deformation and instability.③The potential slip surface passes through the soft soil layer to form an approximate circular arc slip surface.The instability failure of the soft-steep base dump mainly presents the modes of settlement, cracking and slippage.