Abstract: Characteristics of pore structures and development difficulties of the low-permeability gas reservoirs in the Zhuhai Formation in Wenchang A Sag of the Zhujiangkou Basin were studied with the method of constant speed mercury injection. Results show that: ① pore radius are similar for the cores with different permeability, throat is the main factor determining the reservoir permeability in the study area. The mainstream throat radius is the key physical parameter to be used to evaluate percolation ability and development difficulty of a low permeability reservoir; ②1×10^-3μm² is is a critical value for a low permeability gas reservoir. While the permeability of gas reservoir is higher than 1×10^-3μm², the development difficulty of Zhuhai Formation in Wenchang A Sag is getting smaller; and while the permeability of super-low permeability reservoirs near is lower than 0.1×10^-3μm², the development difficulty of Zhuhai Formation in Wenchang A Sag (ZH₃ of Wenchang WC-Y1 well) is greater.