The　dynamic　responses　under　an　ambient　vibration　for　eight　half-through　and　through　concrete-filled　steel　tubular　(CFST)　arch　bridges　are　measured.　The　Stochastic　Subspace　Identification　(SSI)　method　presented　by　Katayama　is　used　for　experimental　modal　analyses,　and　the　feasibility　of　this　method　is　verified　by　comparing　with　the　results　obtained　by　the　Maximum　Entropy　Method.　Compared　with　the　experimental　modal　analysis　by　SSI　method,　the　correctness　of　theoretic　modal　analysis　by　the　finite　element　method　is　confirmed.　The　influence　of　some　parameters,　such　as　the　arch　main　span,　cross　section　and　deck　system,　is　discussed　on　the　in-plane　vibration　properties　of　CFST　arch　bridges.　The　limitation　of　the　statistical　approximate　formula　for　the　in-plane　first　frequencies　of　CFST　arch　bridges　is　pointed　out,　and　the　static　method　based　on　the　Rayleigh　energy　method　is　presented,　which　can　predict　and　check　in-plane　low　frequencies　of　half-through　and　through　CFST　arch　bridges.