The　index　system　of　comprehensive　risk　assessment　for　seismic　performance　of　urban　water　distribution　system　was　established　from　the　following　aspects　as　earthquake　and　engineering　geology,　external　and　internal　factors　of　water　supply　network,　water　quality,　and　so　on.　According　to　many　uncertainty　factors　such　as　randomness,　fuzziness　and　the　shortage　and　imprecision　of　datum　information,　Monte-Carlo　method　was　presented　to　simulate　triangular　fuzzy　numbers　for　transforming　the　operations　of　triangular　fuzzy　numbers　and　their　functions　into　the　conventional　operations　of　real　numbers,　and　then　an　aggregative　risk　assessment　method　using　stochastic　simulation　and　triangular　fuzzy　numbers　for　seismic　performance　of　urban　water　distribution　system　was　established.　The　application　results　showed　that　the　assessment　expressed　by　confidence　intervals　can　provide　more　reliability　information　than　that　of　common　evaluation　methods,　and　can　also　be　applied　to　comprehensive　risk　assessment　problems　of　different　seismic　performance　of　urban　water　distribution　system　affected　by　many　uncertainty　factors.