The reservoirs of Xujiahe Formation in northeastern Sichuan basin，with low porosity and permeability，are typical tight sandstone reservoirs. The exploration results show that the main types of reservoir fluid are gas（gas with low resistivity），gas-bearing water，dry layer and water. But there are difficulties in accurately identifying the types of fluid in tight sandstone reservoirs，which has became a restriction during the exploration and development of Xujiahe Formation. Based on the above problems，after analyzing the reasons of the difficulties in accurately identifying reservoir fluids，two types of regular methods were proposed to identify Xujiahe tight sandstone reservoir fluids in northeastern Sichuan basin and the advantages and disadvantages of each method were analyzed. At the same time，the paper attempted to use Fisher discriminatory analysis to identify reservoir fluid. The canonical functions derived from Fisher discriminatory analysis could be used to easily distinguish reservoir fluid. The coincidence of the obtained results were 92.3% with the actual production situation，which showed that better effects could be obtained by this method in identifying types of fluid in tight sandstone reservoirs in the work area.