Abstract：The lower limit parameters of a reservoir play an important role in the reservoir exploration and development. Conventional methods are greatly limited in determining the lower limits of low porosity and low permeability reservoirs. In this paper, based on the mercury penetration experiment, water-blocking experiment and NMR experiment, the methods of determining the lower limit parameters within the low permeability reservoir are proposed by using the minimum flow pore throat radius. That is, considering low permeability reservoir's microscopic characteristics, the minimum flow pore throat radius of the gas-bearing section is first determined, and then the relationships between porosity, permeability and median radius are established in order to calculate the low limits of porosity and permeability. Using this method, the lower limits of porosity and permeability of the Xujiahe Formation (T3x) gas reservoir in Hebaochang area are determined: the lower limits of porosity in T3x2, T3x4 and T3x6 Formation are 5.5%, 5% and 3.8%, and the lower limits of permeability are 0.03×10-3, 0.11×10-3 and 0.12×10-3?滋m2.