Abstract: A physical effect hypothesis based on the microscopic mechanism of gas hydrate formation in the surfactant solution is presented.The hypothesis assumes that the surfactant could alter the thermodynamic conditions of hydrate formation, that is to say, the effect of restriction of surfactant micelle on gas molecule dissolved in it and water molecule absorbed around it is equivalent to the reduction of system temperature.Phase equilibrium parameters of hydrate formation were measured in three different kinds of gasliquidcoalgas hydrate reaction systems composed of three different surfactant solutions (T40, 0.001 mol·L^-1; T40, 0.002 mol·L^-1; T40/T80, 0.001 mol·L^-1), respectively.Comparison of the experiment data with the calculated value of the phase equilibrium theory in the same condition indicated that the thermodynamic conditions were changed evidently when the surfactant was added.For example, in the system with T40/T80 added, when the pressure was 22.67 MPa, the phase equilibrium temperature of hydrate formation could reach 22.6℃, which was 2.1℃ higher than that in pure water.