When analyzing the effect of nitrogen injection assisted steam stimulation on the basis of the same amount of steam injection, many scholars have ignored the effects of total heat injection of steam stimulation. Through the analysis of characteristics of heavy oil reservoir in Gudao oilfield under the same heat injection, we select reservoir thickness at 2-5, 5-8, 8 m above, and permeability of 500×10-3，1 000×10-3，2 000×10-3 μm2, corresponding to a porosity of 30%, 35% and 40% respectively. In experiments, we compare the nitrogen-assisted steam stimulation performance by using numerical simulation technology through three aspects: oil increment, heating radius and the degree of bottom water coning. At last, new methods of selecting zone for nitrogen-assisted steam stimulation are ac?complished, which consider the bottom water and viscosity. The methods can be utilized to effectively analyze the feasibility of nitrogen-assisted steam stimulation in heavy oil reservoir. Study has shown that the nitrogen-assisted steam stimulation is suitable in eastern Ng3 and Zhongerbei Ng5 and not applicable in Gubei Ng3.