An apparatus for measuring high pressure liquid-liquid equilibria was established. In order to diminish disturbance for the equilibration, the capillaries of stainless steel with 0.7 mm in inside diameter were used to take samples. The taken samples were totally evaporated into gas chromatography. The accuracy of the apparatus was verified by duplicating the literature data. Liquid-liquid equilibrium data for pseudo-ternary mixture of water-2-butanol-C-4-hydrocarbon (the mixture of n-butane + trans-2-butene + cis-2-butene) were experimentally determined under pressure 8 MPa and at temperatures from 403.2 to 443.2 K. The measured liquid-liquid equilibrium data could be correlated by modified Redlich-Kwong (R-K) equation of state.