The SAGD pilot test in Guantao oil reservoir, Du 84 block Liaohe oil field has achieved good results. But the existence of the top water is harmful to SAGD process. Non-Condensable Gas injection with steam (NCG-SAGD) is a beneficial technique for this kind of reservoir. Gas selection is an important step for NCG-SAGD. Based on the high temperature and high pressure phase-equilibrium experimental devices, the solubility of NCG like CH4, CO2 and N2 in super-heavy oil has been measured. Also the thermal property of heavy oil saturated with these NCG were tested separately. A numerical simulator is used to forecast the performance of different NCG in this reservoir, and optimize the operating parameters to maximize the effect of NCG additive. After series of experiments, the main results are as follows: The solubility of the three kind of gases is increasing along with the reduction of the temperature and the increase of the pressure. With the rise of the temperature and pressure, the viscosity of the crude saturated with the three kind of gases will reduce, and the density of the crude saturated with the three kind of gases will also decrease. The dissolving capacity in the Guantao oil and the viscosity reduction effect for the three kind of gases are listed as follows from high to low: CH4>CO2>N2. Simulation results shows that the production process for N2 is the longest because of its good heat insulation property. N2 is determined as the assistant gas in the SAGD technology according to the demands for top-water reservoir and mechanism of NCG-SAGD technology.