Equation of state for mixture methane-carbon dioxide was developed in the form of combination of free Helmholtz energy of components of mixture and the interaction function. Coefficients of equation were determined on the base of experimental data on mixture’s density at temperatures from 193 to 673 K and at pressures up to 100 MPa tacking into account the requirements of phase equilibrium. The thermodynamic behavior of mixture at saturation state was analysed. It was established that the difference of temperatures of saturated vapor and liquid on isobars for different values of composition reach 45 K. The values of coefficient of performance and specific volumetric refrigerating capacity of cycle of one-step refrigerating machine using the mixture СН4-CO2 as refrigerant were calculated.