In　this　paper,　through　the　function　transformation　of　four　disaster　loss　indexes　about　the　dead　number,　the　injured　number,　destroyed　buildings　and　direct　economic　loss　caused　by　earthquakes,　the　standards　to　distinguish　these　disaster　grades　by　using　different　loss　indexes　are　unified.　In　terms　of　the　Unascertained　Measurement　theory　and　concept　of　the　Unascertained　Measurement　Interval,　the　Unascertained　Measurement　Interval　evaluation　model　and　credible　identification　rules　are　established　to　analyze　every　safety　index　for　the　purpose　of　its　reliability,　thus　seismic　disaster　damage　grade　can　be　evaluated.　he　disaster　grades　of　7　important　earthquakes　in　Chinese　mainland　froth　1966　to　1933　are　divided　and　their　disaster　conditions　are　compared　by　using　the　methods.　The　results　show　that　the　methods　basically　can　evaluate　quantitatively　and　accurately　the　seismic　damage　situation　and　the　model　has　more　advantage　than　fuzzy　math　when　disposing　unascertained　factors,　e.g.　less　data　lost　and　more　credible.