Abstract: In the flood insurance,the sample information gotten doesn't accord with the theory requset for the statistical sample.So the Bayesian approach is used,namely according to premium confirmed by priori information,claim frequency and expected claim size are adjusted and corrected combining the new claims sett lement record.Thus premium can be est imated correctly and suits actual risk level.And an example is used to check the feasibility of Bayesian approach.The method and conclusion of the paper can afford reference for project research and business of flood insurance.