A　conditional　probability　density　distribution　surface　(CPDDS)　is　constructed　by　two　functions　in　this　paper.　One　is　the　function　of　population　mean　and　the　stress　level;　the　other　is　the　function　of　standard　deviation　and　the　stress　level.　The　surface　represents　the　probability　density　curve　of　fatigue　life　changing　with　the　stress　level.　A　new　definition　of　fatigue　limit　as　well　as　the　determination　method　is　given　in　this　paper　according　to　the　small　probability　event　of　CPDDS.　The　proposed　method　can　save　considerable　cost　and　time　in　the　determination　of　fatigue　limit.　(C)　2012　Elsevier　Ltd.　All　rights　reserved.