The current evaluation and testing for tight sandstone reservoirs is not as satisfactory as for conventional sandstone, with a low well log interpretation coincidence rate. The fundamental reason is that the reservoir hydrocarbon saturation can not be determined accurately. The calculating methods for the conventional sandstone reservoir saturation are used for the tight sandstone reservoirs and the key of these methods is to obtain high-quality rock electrical parameters. The rock electric parameters for a tight sandstone reservoir are more difficult to obtain because of the small porosity and the complex pore structure, so one often uses the rock electric parameters of a reservoir of higher porosity and permeability in the same area. According to the characteristics of tight sandstone, the gas drive experiments were carried out to study the variations of electric parameters. It is found that a big difference exists in the b, n values between reservoirs of high porosity and permeability and tight sandstone reservoirs. The values of b, n vary in different ranges of water saturation of the cores of 5％ to 10％porosity. Under a high water saturation, the value of b is nearly 1 and the value of n is within a range of 1.3 to 14.1; under a low water saturation, the value of b is within a range of 1.4 to 2.9, the value of n is within a range of 0.5 to 1.7. Since the water saturation is greater than 90% in the high water section, the selection of b, n values of low-water saturation should be careful in well log interpretion. With experimental results being used in a few wells, these results are shown to be consistent with the test results.