Abstract: The oil and gas in Liu-1 Member of Liushagang Fm in Weixinan Sag, Beibuwan Basin are hot points for increasing re-serves and production in Sourth China Sea Oil Field. Based on the analyzing results of reservoir physical properties in the discovered oil & gas fields, it is found that reservoir physical properties are very complicated, not only high porosity and high permeability, but also with medium porosity and high permeability, low porosity and low permeability. The study results indicate that under different depositional systems, microfacies and diagenesis are the main factors influencing the reservoir physical properties. Under different depositional systems, the reservoirs with different microfacies have different physical properties due to influence of the rock com-position, grain sizes, argillaceous content and sorting coefficient. Diagenesis might influence the reservoir physical properties due to compaction and cementation. Due to dissolution, intragranular dissolved pores and feldspar dissolved pores have great influence on reservoir physical properties. Reservoir pore structures have different characteristics under different influence conditions.