Low- permeability sandstone gas reservoirs in offshore basins have low gas content and no obvious lower limit of reservoir physical properties, which is one of the difficult problems in the current exploration scenario. In this paper, the fluid mobility, the lower limit of reservoir physical properties and charging progress of natural gas in the low- permeability sandstone reservoir, LD10 gas field, Yinggehai basin are studied. The results show that three types of reservoirs are developed in the study area: characteristics of the movable type I reservoir is strong dissolution, large pore- throat with the best quality, which is the dominant migration channel. Weak dissolution, medium pore- throat with partially movable are the characteristics of type II reservoir, which has a high proportion of reservoir movable fluid under high power. Tight reservoirs with microporous tube bundle throat is the characteristics of the type III reservoir. Few large pore throats are developed, and the gas saturation varies greatly. The distribution of large pore- throat and reservoir physical properties are the main factors controlling fluid mobility in low- permeability reservoirs. Considering the micro and macro factors, the lower limit of pore- throat radius of low- permeability sandstone reservoirs in LD10 gas field is 0. 1 μm. The lower limit of permeability is 0. 125×10-3μm2. Type III reservoir is tight and can be used as the shielding layer. Type I reservoir is a favorable area for gas accumulation when the natural gas charging power is low or at the initial stage. When the driving force is sufficient, type I reservoir is the dominant migration channel and the accumulation area of gas reservoirs, and the type II reservoir becomes an effective reservoir. The research results can be used for reference to distinguish the effectiveness of low- permeability sandstone reservoirs and predict the favorable area.