Abstract: This paper takes the Yuntaishan tunnel located in Lianyungang as an example. The lithology around the tunnel is single, which consists of a massive of hard granulite and a small amount of weak green schist. The intersection of the structural features releases blocks or wedges which can fall or slide from the surface of the tunnel excavation. This paper considers its discontinuity controlling model. The keyblock theory is used to optimize the design of the tunnel with Unwedge procedure, which includes the choice of hole shape,the trend of the tunnel,support parameters. Through the analysis and calculation,it is indicated that the key block theory is correct and efficient,which is significant to the further study of the optimization of tunnel design in low ground stress regions．