In situ synchrotron radiation X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) measurements were employed to investigate the compressibility and the electronic structure of natural siderite in diamond anvil cells (DACs). No phase transition occurs up to 50.2 GPa at room temperature but a pressure-induced structure evolution from the calcite-type to the NaCl-type can be observed. The axial compression is anisotropic with c-axis more compressible than a-axis. Fe²⁺ undergoes spin state transition (HS→LS) at 44.6~47.1 GPa with volume collapse 8%. Fitting to the Brich-Murnaghan equation of state yields bulk modulus K₀=112(5) GPa and its pressure derivative K₀'=4.6(3). XANES measurement was used for the first time to investigate the electronic structure of Fe²⁺ in siderite. The result implies that no major changes take place in the coordination and the local symmetry of Fe²⁺ until 37.3 GPa; thereafter the HS→LS transition occurs and the LS Fe²⁺ has lower splitting energy and higher probability of electronic transition.