Abstract: Soft-rock tunnels are more and more widely used in metal mines， traffic tunnel and hydraulic projects. Because the soft rock has low strength and poor stability， the tunnels excavated in the soft rocks must be supported immediately. The current stability evaluation methods given in the design specifications cannot be used for the tunnels which should be supported at once. To deal with these problems， the interrelationships of vault deformation and spray stress in the soft-rock tunnel are investigated based on several numerical experiments including the interrelations between different elastic modulus， Poisson ratio， cohesion， internal frictional angle， buried depth， diameter， lateral pressure coefficient， and so on. Based on the interrelationships， a new concept of the stability evaluation of the rock mass is discussed based on the security of the supporting structure， and the reliability has been demonstrated by the water diversion project located at Kuyu in Xinjiang Uygur Autonomous Region. The numerical test results show that all variables have significant influences on the vault deformation and spray stress， especially for the major principal stresses. With the development of the deformation， the principal stress axes are exchanged and the names of major and minor principal stresses interchanged. The major principal stress of shotcrete increases with the increase of elastic parameters and decreases with the increase of strength parameters. The research results can provide a theoretical guidance for the design and construction of the similar soft-rock tunnels.