In　gun　barrel-cradle　structure,　the　presence　of　clearance　usually　changes　the　dynamic　response　of　muzzle　and　results　in　shooting　dispersion　(under　continuous　firing　condition).　The　parameter　estimation　of　such　clearance　nonlinear　system　is　the　prerequisite　for　establishing　quantitative　relation　between　the　clearance　and　muzzle　disturbance.　In　this　paper,　the　restoring　force　surface　(RFS)　method　and　the　nonlinear　identification　through　feedback　of　outputs　(NIFO)　method　are　first　combined　for　parameter　identification　in　a　simplified　barrel-cradle　structure.　With　the　RFS　method,　clearance　value　can　be　obtained　by　analyzing　the　restoring　force　plot.　Then　the　contact　stiffness　can　be　identified　by　using　NIFO　method.　This　identification　process　is　verified　in　a　single-degree-of-freedom(SDOF)　system　with　clearance.　To　adapt　to　the　rigid-flexible　coupled　beam　system　with　clearances　which　is　simplified　from　the　barrel-cradle　structure,　a　modification　for　the　combined　method　mentioned　above　is　proposed.　The　core　idea　of　the　modification　is　reducing　the　continuous　system　to　multiple-degree-of-freedom　(MDOF)　system　to　reserve　the　nonlinear　characteristics　through　modal　transformation　matrix.　The　advantage　of　this　transformation　is　that　the　linear　parts　of　the　MDOF　systems　are　decoupled,　which　greatly　reduces　the　difficulty　of　identification.　The　simulation　results　have　shown　the　effectiveness　of　current　method.