In　order　to　research　the　cause　of　tank＇s　torsion　shaft　fatigue　fracture　prematuely,　the　stress　concentration　on　the　surface　of　a　torsion　shaft　due　to　nolches　was　simulated　by　elastic　finite　element　analysis　method.　The　fatigue　life　of　torsion　shafts　on　which　there　are　notches　of　different　shapes　and　dimensions　under　some　load　spectrum　was　calculated　with　livability　of　99%.　Results　show　that　the　fatigue　life　of　tursion　shafts　will　decrease　sharply　when　long　and　narrow　nothex　appear　on　the　surface　of　a　torsion　shaft.　If　these　long　and　norrow　are　enlarged　to　circular　nortches,　the　fatigue　life　of　a　torsion　shaft　will　be　prolonged　largely.