Yinggehai Basin is an important Cenozoic gas-rich basin on the northern continental shelf of the South China Sea. With the continuous improvement of oil and gas exploration, the exploration targets have been continuously expanded to the middle and deep layers, and good exploration discoveries have been obtained. The Miocene Huangliu and Meishan Formation of Ledong area of Yinggehai Basin are the key strata for gas exploration in the northern South China Sea. Due to the complex geological conditions, difficult exploration conditions and high temperature and overpressure background in Ledong area, it is difficult to define the lower limit of reservoir physical properties, which affects the reasonable classification of reservoirs. Based on the observation and analysis of petrographic thin sections of 188 samples from more than 10 wells in study area, combining the data of logging, mercury injection, formation test and physical property analysis, and reasonably adopting the distribution function curve method, test method, displacement pressure method and empirical statistical method, the lower limit of effective reservoir physical properties of Miocene Huangliu Formation and Meishan Formation in Ledong area is determined. The controlling factors on effective reservoir development were studied, and the main parameters were optimized to finely classify the reservoir. It provides a scientific basis for the exploration of key fields in Ledong area. The results show that：(1) The lower limit of porosity and permeability are 8， and 0.2×10-3μm2 respectively. (2) The physical properties of reservoir in Ledong area are mainly controlled by compaction. Carbonate cementation and dissolution related to deep thermal fluid are the main controlling factors of effective reservoir, otherwise the grain size and sorting of reservoirs controlled by sedimentation have relatively little impact on reservoir physical properties in Ledong area. (3) The Miocene reservoirs in Ledong area can be finely divided into six types: Ⅰ, Ⅰ1, Ⅱ2, Ⅲ, Ⅳ1 and Ⅳ2，of which Ⅰ, Ⅰ1, Ⅱ2 and Ⅲ are effective reservoirs, and Ⅳ1 and Ⅳ2 are ineffective reservoirs.