Big　errors　will　occur　in　the　modeling　by　multimode　methodology　when　the　available　core　physical　parameter　sets　are　insufficient.　In　this　paper,　the　fuzzy　logic　membership　function　is　introduced　to　figure　out　the　values　of　these　parameters　on　any　point　of　lifetime　through　limited　several　sets　of　values,　and　thus　to　obtain　the　neutron　dynamics　equations　on　any　point　of　lifetime.　In　order　to　overcome　the　effect　ofsubjectivity　in　the　membership　function　selection　on　the　parameter　calculation,　quadratic　optimization　is　carried　out　to　the　membership　function　by　genetic　algorithm,　to　result　in　a　more　accurate　neutron　kinetics　equation　on　any　point　of　lifetime.