We propose a service evaluation method based on risk preferences (SEM-RP) for the risk caused by quality volatility. First, complete description rating information according to the interval number theory is made. Then we use risk preference to identify user's perceived risk in order to express different user's risk propensity. After that, service revenue is obtained by calculate service attributes and users' preferences according to the principle of revenue maximization, and finally we get service evaluation rating by calculate service revenue and user's perceived risk. Simulation experiments and results demonstrate that the proposed method can clearly express the characteristics of user's risk preference while expressing user preferences attributes and which have the performance of higher user satisfaction.