Due　to　its　unique　advantages,　coiled　tubing　is　now　widely　used　in　marine　oil　and　gas　exploitation　operations,　while　the　mechanical　behavior　of　coiled　tubing　working　within　a　marine　riser　affected　by　marine　loads　is　still　unknown.　By　building　an　indoor　simulation　experimental　system,　the　mechanics　of　this　pipe-in-pipe　system　was　studied,　and　the　effect　of　the　lateral　excitation　on　the　axial　force　transmission　of　inner　pipe　was　clarified.　It　was　found　that,　when　the　external　excitation　frequency　was　within　the　first　natural　frequency　range　of　the　outer　pipe,　the　external　excitation　would　increase　the　axial　load　transfer　efficiency　of　the　inner　pipe,　and　the　axial　force　transfer　efficiency　of　the　inner　tube　would　reach　the　maximum　when　the　resonance　of　out　pipe　occurred.　The　results　can　be　helpful　on　the　understanding　of　mechanics　of　a　coiled　tubing　working　within　a　marine　riser.　©　2019　American　Society　of　Mechanical　Engineers　(ASME).　All　rights　reserved.