In the present study, CO2 gas and tetra-n-butyl ammonium bromide (TBAB) is adopted to form CO2+TBAB double hydrate at mass fractions w = 0.05 and 0.10. The moles of CO2+TBAB double hydrate are calculated by the variation of pressure of CO2 gas from initial pressure at about 4.03 MPa and the solubility of CO2 in TBAB aqueous solution at various subcoolings of 2.0-5.0 K. In addition, the formation characteristics of CO2+TBAB double hydrate are observed by the visualization, and it is verified to be a type B double hydrate. The kinetics of CO2+TBAB double hydrate formation at w = 0.05 and 0.10 is determined by the normalized rate of hydrate formation in the hydration process.