Ascertaining the attributes similarity between the problem case and cases in the case base is the key of case-based reasoning. Considered the problem of similarity calculation models, analyzed several existent models and brought out a mended range similarity calculation model. This model can deal with the problem that perceptive information and attributes information of cases in case base are both uncertain and incomplete. Demonstrated the calculation model be the same with tiny ranges similarity in the certain range. United the plan reasoning problem of a certain submarine confront flooding assistant decision-making system, compared the calculation results deduced by several existent models, proved that the calculation model can enhance the case similarity sensitivity.