The structural stability of methane hydrate under pressure at room temperature was examined by both in-situ single-crystal and powder X-ray diffraction techniques on samples with structure typesⅠ,Ⅱ,and H in diamond-anvil cells.The diffraction data for typesⅡ(sⅡ) and H(sH) were refined to the known structures with space groups Fd3m and P6_3/mmc,respectively.Upon compression,sⅠmethane hydrate transforms to the sⅡphase at 120 MPa,and then to the sH phase at 600 MPa.The sⅡmethane hydrate was found to coexist locally with sⅠphase up to 500 MPa and with sH phase up to 600 MPa.The pure sH structure was found to be stable between 600 and 900 MPa.Methane hydrate decomposes at pressures above 3 GPa to form methane with the orientationally disordered Fm3m structure and iceⅦ(Pn3m).The results highlight the role of guest(CH_4)-host(H_2O) interactions in the stabilization of the hydrate structures under pressure. The structural stability of methane hydrate under pressure at room temperature was examined by both in-situ single-crystal and powder X-ray diffraction techniques on samples with structure types I, II, and H in diamond-anvil cells. Diffraction data for types II s II) and H (sH) were refined to the known structures with space groups Fd3m and P6_3 / mmc, respectively.Upon compression, sⅠmethane hydrate transforms to the sⅡphase at 120 MPa, and then to the sH phase at 600 MPa.The sⅡmethane hydrate was found to coexist locally with sIphase up to 500 MPa and with sH phase up to 600 MPa. The pure sH structure was found to be stable between 600 and 900 MPa. Methane hydrate decomposes in pressures above 3 GPa to form methane with the orientationally disordered Fm3m structure and ice VII (Pn3m). The results highlight the role of guest (CH_4) -host (H_2O) interactions in the stabilization of the hydrate structures under pressure.