Abstract: The phase equilibrium data of cyclopentane (CP)-methane hydrates in NaCl aqueous solutions were measured by pressure search procedure with a viewable experimental apparatus for gas hydrate. The formation and dissociation heats of CP-methane hydrates were calculated based on these phase equilibrium data using Clausius-Clapeyron equation. The formation of hydrate became markedly easier after CP addition to methane. At temperature higher than the quadruple point of pure CP hydrate，CP-methane hydrates could be formed at a low pressure when methane was used as a help gas. The phase equilibrium pressure of CP-methane hydrates increased with the increase in temperature，and linearly increased with NaCl concentration in solution. Moreover，the effect of temperature and NaCl concentration was more obvious at a higher temperature. The formation and dissociation heat of CP-methane hydrates decreased with the increase in temperature and NaCl concentration.