Based　on　the　time　function　of　the　economic　variable　of　the　project　and　probability　distribution　of　me　predicted　value,　this　paper　put　forward　a　calculation　formula　of　the　economic　risk　indicator　of　BOT　project.　By　using　the　simulation　computing　technology　to　get　the　expected　value　of　every　economic　risk　indicator　of　BOT　project　and　probability　distribution,　than　measure　the　economic　risk　of　investment　project,　according　to　the　taste　degree　to　the　risk　of　invest　operator,　than　make　the　decision　on　investment　item.　Basing　on　the　of　time　function　of　the　economic　variable　and　the　predicted　value　of　cumulative　distribution　function,　this　paper　proposes　the　mathematic　expression　of　every　economic　risk　indicator,　and　the　estimate　method　of　the　economic　risk　of　project　by　using　the　simulation　method　to　obtain　the　expected　value　of　every　economic　risk　indicator　of　BOT　project　and　cumulative　distribution　function　basing　on　the　risk　preference　of　the　investors　and　operators,　analyze　the　economic　indicator　value　with　the　risk　tolerance　that　can　be　accepted,　offer　more　precise　decision　to　investor.