Abstract: Tight sandstone gas is an important type of unconventional oil and gas resources, but industry standards or regulations for tight gas reserves estimation have not yet introduced.Based on a brief comparison of resource evaluation methods of unconventional and conventional oil and gas, and a discussion on tight sandstone gas resource evaluation methods at present, this paper puts forward an uncertainty volume method for tight gas resource estimation.Considering tight sandstone gas reservoirs’ characteristics of quasi-continuous spatial distribution, difficulty in determining gas-bearing area, and the strong heterogeneity of the effective thickness and reservoir parameters, we argue that it’s more reasonable to estimate tight gas geological reserves using uncertain probability volume method.Taking He-2 member in Kangning area of the Ordos basin as an example, by using geostatistics stochastic simulation, P90(low), P50(middle), P10(high) probability of different geological reserves are calculated based on volume method.The geological reserves are estimated in different exploration well numbers in accordance with the completion time order, which show that the reserves estimation results have been related to the drilled well number; for reducing exploration risk, the uncertain probability volume method should be used to calculate tight gas geological reserves before reaching the saturation exploration point.Using uncertain probability volume method to calculate geological reserve could facilitate the healthy and orderly exploration and development of tight sandstone gas resources.