Separation of a mixture of CH₄ + C₂H₄ gas by forming hydrate in ethylene production has become of interest, and the dissociation behavior of (CH₄ + C₂H₄) hydrate is of great importance for this process. The hydrate formation rate could be increased by adding a small amount of sodium dodecyl sulfate (SDS) into water. In this work, the kinetic data of CH₄(18.5 mol%)+ C₂H₄(81.5 mol%) hydrate decomposition in the presence of 1000 mg?L^-1 SDS at different temperatures and pressures were measured with the depressurizing method using a sapphire cell apparatus. The experimental results show that the dissociation rate of (CH₄ + C₂H₄) mixed gas hydrate was large at high temperature and low pressure, and temperature had great influence on the dissociation rate at high pressure. A kinetic model for hydrate dissociation was proposed and the calculated results from the kinetic model were in good agreement with the experimental data. The activation energy for dissociation of the (CH₄ + C₂H₄) mixed gas hydrate was determined to be 43.9 kJ?mol^-1, which is lower than that of methane (81.0 kJ?mol^-1) and ethane (104.0 kJ?mol^-1) hydrate in water (Clarke and Bishnoi, 2004). As the similar molecular dimensions between ethane and ethylene, the close activation energy need to be provided for ethylene hydrate dissociation. The obtained activation energy of the (CH₄ + C₂H₄) mixed gas hydrate dissociation indicates that the dissociation of the (CH₄ + C₂H₄) mixed gas hydrate is easier than that of pure CH₄ or C₂H₄ gas hydrate.