Abstract: Characteristics of micro-pore structures and factors controlling the low-permeability reservoirs in the Huangliu Formation in the Dongfang area of the Yinggehai Basin were studied by mercury injection experiments with constant rates.The average pore radius of the reservoirs is about 100-140 μm, the average throat radius is about 1-5 μm, and the mainstream throat radius is less than 5 μm.The permeability is not correlated with pore radius, and reservoirs with different permeabilities can have similar pore radius distributions.In contrast, permeability is strongly associated with throat radius and its distribution.The throat radius and the mainstream throat radius decrease as permeability becomes lower, and the distribution range gets narrower.The throat to pore ratio increases as permeability decreases, and its distribution range becomes wider.The low permeability of rocks in the study area can be explained by their small throat radius.Strong compaction effects and authigenic clay minerals are the main factors which undermine the micro-pore structures and make the permeability low.