A thermodynamic model for wet steam and flue gas blending and injection process was constructed according to the energy and mass conservation principles. The fugacity coefficients were calculated based on the equation of state, and an in-house code of vapor and liquid flash calculation for three components (N₂, CO₂ and H₂O) was constructed. The code was verified with some two components phase equilibria experimental results and a theory equation. With the code, the steam quality and temperature of the wet steam and flue gas after blending were calculated. It was found that the steam quality can be increased or decreased dependent on its value before blending. There is a threshold value of the steam quality, which is affected by pressure, temperature and flue gas compositions. When the steam quality before blending is less than the threshold value, the steam quality after bending will be increased, and when the steam quality is bigger than the threshold value, it will decrease during blending. The temperature of the blended mixture will be reduced, and the lower the injecting steam quality, the larger of the blending temperature reduction. The mole fractions of N₂ and CO₂ in water phase were at around a few thousandths and will be increased when the injecting steam quality decreases.