Abstract: Method of prototype study of strain of dam foundation rock and results are presented; Effective modulus of elasticity of foundation rock is obtained by counter-deduction and the stress is calculated. Using method of step regression analysis the mathematical model of stress of foundation rock is set up and principle and method for safety prediction of strain of dam foundation rock and for control of the strain in operation period are proposed. Calculation of dam stability and evaluation of safety from the observed strain of foundation rock are conducted.