Reservoir protection is an essential condition for economical and efficient exploration of the tight sandstone gas reservoirs. Now，the main method to evaluate the reservoir protection effect of the drilling fluid is permeability recovery，but it is so simple that cannot evaluate the long-term impact of drilling fluid on the gas reservoir productivity，which is a process of long-term interaction between two phases of gas and fluid. While the relative permeability experiment of the core before and after being polluted by the drilling fluid can be a good remedy for the problem. According to the reservoir characteristics of the Shenmu block in Tarim oilfield，comprehensive analysis and comparison were done on the variation of core permeability recovery value，relative permeability curves and oil and water saturation used in sandstone module of CMG numerical simulation software before and after pollution of core by polysulfonated potassium drilling fluid and oil-based drilling fluid. Reservoir protection effect of the polysulfonated potassium drilling fluid and oil-based drilling fluid was simulated. The impact of various drilling fluids on the gas reservoir productivity was matched and the productivity can be an evaluation index of formation damage degree. The comprehensive evaluation results show that the oil-based drilling fluid has a better effect of reservoir protection than the polysulfonated potassium drilling fluid. The cumulative gas production will be increased by 15%.