Abstract: Based on that the strength of rock micro-unit obeys the Weibull random distribution, this paper presents a damage constitutive model reflecting the full process of rock failure. Then, the approach of establishing rock strength theory using the method by which the extremum is obtained for pluralistic function is discussed according to the concept of yielding or failure of rock and a rock damage statistical strength theory. A way to establish strength theory of rock have been founded elementarily. It is of obvious superiority compared with practical results and other theories.