The wettability of gas reservoir has great influence on original occurrence of oil，single well production and ultimate recovery. By comparing tight sandstone reservoir core and steel core，the water invasion degree was simulated through evaluating the variation of oil/water volume ratio，and the change of wettability of the tight sandstone gas reservoir under circumstances of water invasion with low temperature was researched. The results show that the oil/water volume ratio decreased continuously and the probability of contact between sandstone surface and oil components in the gas reservoir was reduced after water invasion in the gas reservoir，which results in hydrophilicity instead of hydrophobicity in both steel core and rock core of the tight sandstone gas reservoir. The hydrophobicity of the steal core is weaker than that of the sandstone core under the same water invasion degree. The reason is that the tight sandstone has clay minerals，and the clay minerals can absorb some of the oil components and make more surface area hydrophilic. The rising rate of the surface contact angle of the gas reservoir sandstone will increase with the volume of water invasion.