Abstract: A novel method of reliability evaluation based on the stochastic process and cloud theory is proposed to solve the problems of the uncertainty in the reliability evaluation and the difficulties of the transformation between qualitative information and quantitative information in the reliability evaluation. The cloud theory is merged into the stochastic process reliability analytical method, and the system state transfer is described using cloud theory. At the same time, the cloud scale of the qualitative evaluation is constructed, and the quantitative variable and the qualitative variable in the system reliability evaluation are corresponded. The randomness and the fuzziness of the system reliability evaluation are considered in the method and the relationship between the quantitative variables and the qualitative variables is analyzed. The result is a linguistic value and is intuitive. Through the method, the corresponding relationship between the quantitative variables and the qualitative variables is found, and the linguistic value is understood and used in the process of the system evaluation. Finally, an example validates the feasibility of the method.