Abstract: The reliability of computers is tightly related to its suitability and its working conditions. Because the working conditions are usually described by qualitative, fuzzy words, and the suitability is usually described with only a outline, it’s difficult to evaluate the reliability count for the effects of environmental factors. By mapping qualitative linguistic suitability word into quantitative values and translating the uncertainty working conditions into a fine changeable variable drops using cloud models, a new evaluating way is proposed taking suitability and working conditions into account. It may solve the reliability evaluation problems of military computers working in changeable conditions.