uzzyRPNmodel,inordertoallowvalidandmeaningfulcomparisonsamongdifferentfailuremodesinFMEAtobemadeisinvestigated.ThefuzzyRPNmodelisviewedasanassessmentormeasurementmodel,whichissubjectedtosometheoreticalpropertiesofalengthfunction,e.g.monotonicity,sub-additivityandetc[].InvestigationinthispaperfocusesonmonotonicitypropertyofthefuzzyRPNmodel.ThefuzzyRPNmodelisfirstlypresented.MonotonicitypropertyinFISandasufficientconditionforaFIStobemonotoneisalsoreviewed.MonotonicitypropertyforthefuzzyRPNmodelisfurtherdefined.Inthispieceofwork,thesufficientconditionsforaFIStobemonotone,aspointedinvarioussources[,,,],isappliedtothefuzzyRPNmodel.ThesufficientconditionspointedoutthatforaFIStobeofmonotonic,twomathematicalconditionsareneeded.Condition()canbeviewedasamethodhowmembershipfunctionshouldbetunedinordertoensurethefuzzyRPNtobeofmonotonicityproperty.Condition()highlightstheimportantofhavingap和q是可以区分,对p