In the view of problems that reservoir petrologic characteristics, microscopic pore genetic types and their controlling factors have not been researched clearly in the fourth member of Lower Cretaceous Quantou Formation in GD area, southern Songliao Basin, by comprehensive application of the data of thin section, scanning electron microscope and clay mineral, this paper studied the reservoir pore types and controlling factors. The pores of Quan 4 member in GD area are mainly post compaction residual pores, post cementation residual pores, dissolved intergranular pores and dissolved intragranular pores. The dissolved intergranular pores are formed by the dissolution of intergranular matrix, cements, feldspar and debris, and the dissolved intragranular pores are formed by internal corrosion of feldspar and eutectic part in debris. Tectonic fractures developed locally are quite important to reservoir physical properties. The present pores genetic types are closely correlative with the depositional environment and diagenesis. The sedimentary conditions determine its petrologic feature of fine-grained and mud-rich, and further control the reservoir features of pore primary pores in this area. Compaction is decisive for the remaining primary pores size and volume, cementation is the main factors for destroying the primary pores, and carbonate cementation provides material base for later dissolution. Dissolved pores formed by dissolution are of very important contribution in enhancing the porosity. Based on the analysis of rock thin section and scanning electron microscope, it is considered that the Quan 4 member belongs to reservoir with mixed pores, remaining primary intergranular pores are the dominated reservoir space, later dissolved pores have a crucial role in improving the reservoir properties, and micropores in matrix are of little importance for reservoir properties.