Operational risk is one of the primary risks in banks.Owing to the key function of the experts' knowledge to the operational risk measuring,it's important to use the uncertainty reasoning theory to quantitate the information from experts.This paper uses the DS evidence theory to establish the distinguish framework,collect the information from experts,and adopts the weighted average coefficient to modify the Dempster formula that use to find the final measurement of operational risk.It shows the validity of this method though the empirical research on three commercial banks in China.