The control of large deformation of surrounding rock and supporting structure of soft rock tunnel with high geostress and high rheology conditions is very important. Hence, the action mechanism of prestressed yielding anchor cable in large deformation control of the tunnel is studied through theoretical and numerical analysis. The study includes two aspects as follows: one is the study on mechanical properties of new type of yielding anchor plate under low pretightening force and low surrounding rock pressure to meet the requirements of flexible support; the other one is the study on the stress bearing performance of supporting structure improved by prestressed anchor cable under high pretension condition after yielding pressure to realize the function of rigid support. The study results show that: (1) The prestressed anchor cable can increase the radial resistance of tunnel wall and improve the stability of surrounding rock by applying pretension force. (2) The main effect of prestressed anchor cable on supporting structure after yielding pressure is to reduce the span, thus to improve the stiffness and bearing capacity of supporting structure. (3) The deformation of surrounding rock, initial support structure and prestressed yielding anchor cable is coordinated and mechanically coupled to form "soft first and hard afterwards" support system.