The synergistic effect of thermodynamic promoter tetrafluoroethane (R134a) and kinetic promoter sodium dodecyl sulfate (SDS) can significantly improve the phase equilibrium conditions required for CO 2 hydrate formation and promote rapid generation of CO 2 hydrate. Based on this, this study investigates the influence of SDS and R134a synergy on the separation of CO 2 / H 2 mixed gas using the hydrate method. The research reveals that without SDS addition, R134a hydrate forms first at the gas−liquid interface before CO 2 hydrate induction, hindering gas−liquid exchange. The addition of SDS can inhibit the formation of the hydrate film, enhance the initiator effect of R134a in the CO 2 hydrate formation process, accelerate the nucleation of CO 2 hydrate, and thus synergistically strengthen the separation of CO 2 /H 2 mixed gases. Hydrate formation can be achieved at a concentration of 100 ppm of SDS solution, and the synergistic growth effect of R134a and CO 2 hydrate becomes more significant with increasing SDS concentration. Optimal separation efficiency and maximum H 2 concentration are achieved at 500 ppm of SDS, with 42.29 and 54.88% separation efficiency and H 2 concentration, respectively. Decreasing the initial charge temperature has little impact on separation efficiency but significantly reduces the induction time, reducing it to 3 min at 12 °C. This study improved the separation efficiency of CO 2 and H 2 mixed gas, providing a better reference for hydrogen purification by the hydrate method.