Elastically　mounted　flexible　membrane　roofs　exposed　to　flows　are　prone　to　vortex-induced　vibrations　and　even　aero-instability　due　to　the　strong　fluid-structure　interaction　(FSI).　This　study　is　to　investigate　the　FSI　mechanism　in　the　saddle-shaped　membrane　structure　over　a　range　of　Reynolds　numbers　and　wind　directions　in　laminar　flows,　by　bridging　structural　vibration　responses　and　flow　dynamics.　The　aeroelastic　characteristics　of　membrane　structures,　including　statistics　of　displacement　responses,　oscillation　frequency,　and　oscillation　damping　ratios,　were　identified　from　the　perspective　of　time　and　frequency　domains.　Simultaneously,　the　particle　image　velocimetry　system　was　employed　to　visualize　the　flow　features,　including　velocity　vector,　turbulence　intensity,　and　vortex　evolution　in　both　space　and　time.　The　flow　modes　were　further　decomposed　by　proper　orthogonal　decomposition　(POD)　to　capture　the　salient　aspects　of　the　flow.　Three　patterns　of　POD　modes　are　identified,　and　the　first　mode　plays　the　dominant　role　in　POD　modes.　It　showed　that　as　the　wind　Reynolds　number　increases,　the　space　between　the　shear　layer　and　membrane　surface　would　be　narrowed,　and　resultantly　the　vortices　turn　out　smaller　in　scale　and　closer　in　space.　This　trend　leads　to　an　increase　in　the　frequency　of　vortex　shedding　and　a　stronger　FSI　effect.　When　the　frequency　of　vortex　shedding　approaches　the　fundamental　frequency　of　structures,　the　vibration　of　the　membrane　would　be　shifted　from　turbulent　buffeting　to　vortex-induced　resonance,　featured　with　lock-in　frequency,　significant　amplified　displacement,　and　negative　aerodynamic　damping　ratio.