Thick tight sandstones in the Silurian period in the eastern Manjiaer sag have broad prospects for natural gas exploration，but there are few studies on reservoir characteristics of the tight sandstone at present. Based on comprehensive utilization of thin-section identification，EPMA，SEM，X-ray diffraction，mercury injection and physical property analysis，the reservoir characteristics of the tight sandstones were studied. Compared with conventional sandstone reservoirs in the eastern Manjiaer sag，the tight sandstone reservoirs have the following characteristics：①great burial depth；②low compositional maturity，low textural maturity，high content of debris and interstitial material；③poor physical properties（porosity is 5%-10%，permeability is 0.1×10-3-1×10-3 μm2）；④reservoir space types mainly include primary intergranular pore，intergranular dissolution pore and micropore，and the pore structure is poor in general；⑤clay mineral composition are dominated by reticular illite smectite mixed layer，chlorite and illite；⑥severe diagenesis and the diagenetic stage is from B substage of middle diagenetic stage to late diagenetic stage. The physical property of the reservoirs is influenced by various factors such as deposition，diagenesis and structure. The factors such as near source deposition，low compositional maturity，low textural maturity and argillaceous matrix filling are not favorable for the preservation of the most of primary pores. The compaction is the main factor resulting in the loss of porosity，and calcite cement and quartz secondary enlargement lead to porosity reduction. Partial dissolution and a few structural fractures improve the reservoir physical property.