To　better　understand　the　mechanics　of　coiled　tubing　working　within　the　risers　connected　to　Floating　liquefied　natural　gas　(FLNG),　this　paper　studied　a　specific　marine　pipe-in-pipe＇　system　with　a　low　diameter　ratio.　The　experimental　results　showed　that　the　axial　load　on　the　inner　pipe　of　an　unfixed　system　increased　with　the　increase　in　injected　length.　In　this　case,　the　force-in＇　was　always　larger　than　the　force-out＇.　The　changing　trend　of　force-in　and　force-out　within　the　unfixed　system　was　essentially　found　to　be　stable　after　a　sinusoidal　buckling　of　the　inner　pipe.　Even　though　the　magnitudes　of　force-in　and　force-out　did　not　increase　a　lot,　the　injected　length　increased　significantly.　Relationship　of　force-in,　as　well　as　force-out,　between　fixed　and　unfixed　system　when　the　pipe　was　buckled　sinusoidally　and　helically　was　found.　The　results　help　in　working　of　a　coiled　tubing　within　small　diameter　marine　risers.