For an extra heavy oil reservoir with top water in Liaohe Oilfield, it is inefficiently and hard to produce by conventional thermal recovery. In this regard, the numerical modeling software – CMG is used to analyze the recovery of this reservoir by Steam-Assisted Gravity Drainage (SAGD) and Steam and incondensable gas-assisted gravity push (SAGP). The production indicators, development effects and distribution of field parameters of these two techniques are contrasted and analyzed, and the injection and production parameters for application of SAGP in wells are optimized. The study shows that, for this extra heavy oil reservoir with top water, SAGP is more effective than SAGD, and the former can reduce the steam demand, improve the oil/steam ratio (OSR), prolong the development and enhance the recovery. It is recommended, during application of SAGP on site, to inject nitrogen at volume fraction of 30-40% and when the steam chamber expands to a section with 1/3 net pay thickness away to the top water.