The invention discloses a detection method and system for user exceed authority sensitive data access behaviors. The system comprises the steps that flow data is collected in real time from a switch; the flow data is restored to SQL data; user behaviors of users accumulated within a certain period of time are adopted as a training data set of a naive bayes algorithm, and the standard probability of user names and user behaviors conforming to the corresponding role type is calculated; the behavior probability of newly-added user names and user behaviors conforming to the corresponding role types is calculated; whether the deviation between the behavior probability of the user behavior of the current role type and the standard probability is larger or not is judged, and if yes, it illustrates that the user accesses data in an exceed authority mode. The flow is restored to a user SQL operation, the operation content accumulated in the certain period of time is adopted as training data, the role of each user is defined in the training data, and the behavior habit of each role is built; when the user access behavior and the user role are not matched, whether the user accesses sensitive data in the exceed authority mode or not is judged.