By　using　function　one　direction　S-rough　sets　(function　one　direction　singular　rough　sets),　the　concept　of　one　direction　rough　law　is　proposed,　where　one　direction　rough　law　is　the　law　pair　{w(x).,　w(x)-)　composed　by　w(x)-　and　w(x)-.　If　the　attribute　set　{α.,　α-)　of　function　one　direction　S-rough　sets　changes,　then　one　direction　rough　law　{w(x)-,　w(x)-　)　will　change,　too.　By　employing　ellipse　curves,　the　concept　of　one　direction　rough　law　security　is　presented,　the　security　theorem　of　one　direction　rough　law　is　proposed　and　the　applications　are　given.　One　direction　rough　law　security,　which　is　generated　by　the　intersection　and　penetration　between　function　one　direction　S-rough　sets　and　ellipse　curves,　is　a　new　applied　research　direction　of　function　S-rough　sets.