The　Grey　system　method　is　firstly　applied　to　predict　the　buckle-cable　forces　in　lifting　the　arch　rib　making　by　steel　tube　of　long-span　CFST　arch　bridge,　and　the　grey　predictive　system　has　been　established　by　taking　the　ratio　of　the　actual　buckle-cable　force　to　the　computational　value　as　initial　data.　The　system　uses　the　GM(1,　1)　model　to　seek　parameter　and　mimesis　list　of　originality　list,　assesses　the　model　precision　by　the　ratio　of　the　mean　square　deviation　and　the　probability　of　small　aberration,　then　educe　the　forecast　value　of　the　next　sections　buckle-cable　forces.　The　basic　principles,　detailed　application　steps　and　effect　are　introduced　combining　with　the　construction　of　a　long-span　CFST　arch　bridge.　The　result　indicates　this　way　suffice　the　engineering　demand,　and　it　offers　reference　for　the　type　alike　engineering.