As　widespread　usage　in　engineering,　the　simplified　Bishop　method　is　used　to　establish　the　limit　state　function.　Considering　the　unit　weight,　cohesive　strength　and　internal　friction　angle　as　random　variable,　the　utility　optimal　method　as　well　as　the　Microsoft　Excel＇s　solver　are　applied　to　solve　the　reliability　index,　which　can　avoid　the　problems　of　orthogonal　transformation　and　derivation　of　the　limit　state　function.　For　the　slope　of　granite　residual　sandy　clay　in　Fujian　Province,　the　reliability　analysis　is　carried　out.　By　comparison　the　results　of　non-correlation　and　correlation　between　parameters,　it　is　shown　that　the　reliability　correlates　with　not　only　the　mean　value　of　parameters,　but　also　the　coefficient　of　variability　and　the　correlation　between　parameters　which　have　a　major　influence　on　it.　Thus,　there　is　a　possibility　of　instability　while　the　slope　is　considered　as　stability　by　the　traditional　safety　factor　calculation　method.