Abstract: The physical property lower limit for mining of tight oil reservoir is becoming lower and lower, gradually approaching that of accumulation filling. Therefore, it is significantly important to accurately determine such lower limit. The bound water film thickness plays a key role in the determination, while the surface area of bound water can be obtained accurately by nitrogen adsorption experiment. There are quite a few defects despite many methods to determine the volume of bound water film. Through investigating various methods, the rock-electric experiment which simulates the formation pressure and temperature is finally adopted, combined with the Archie formula to calculate the saturability, then the volume and finally the thickness of bound water film. The method can well simulate the strata environment, with result closer to the true value, thus the obtained bound water film thickness is more accurate. The low limit of pore throat mean radius is determined by establishing its relation to the bound water film thickness. Then, with principle of statistics, the relation between the pore throat mean radius and permeability is set up to finally decide the low limit of porosity filling and permeability of tight oil reservoir. The results prove to be accurate according to the mercury injection curve.