The　performances　of　material　fatigue　can　be　illustrated　by　the　S-N　curve,　the　p-S-N　curve　and　the　fatigue　limit,　which　are　very　important　to　engineering　and　the　mechanical　design.　Recently,　the　author　proposed　a　new　method　to　determine　a　conditional　probability　density　distribution　surface(CPDDS)　of　the　material,　and　the　surface　can　reflects　most　properties　of　the　material＇s　fatigue.　Methods　to　obtain　the　theoretical　fatigue　limit　and　the　p-S-N　curve　are　introduced　in　this　paper　on　the　basis　of　previous　study.　The　methods　are　applied　on　the　fatigue　test　data　of　C45　steel,　and　the　p-S-N　curves　that　obtained　by　various　methods　are　compared　in　this　paper.　©　(2013)　Trans　Tech　Publications,　Switzerland.