Lower limits of porosity and permeability for oil accumulations can provide major parameters for the oiliness evaluation of tight sandstone reservoir, and important guidance for exploration discovery of tight oil of Ordos Basin which has big exploration potential. Many data including mud logging, log data, well test and production test, physical property, mercury intrusion, fluid inclusion, thin section examination, SEM and so on were applied to determine porosity and permeability cutoffs of effective reservoir in the Chang 7 member, southeastern Shaanbei Slope, Ordos Basin, and critical accumulation period. By adding the loss of porosity after oil accumulation to current lower limit value of effective reservoir, lower limits of porosity and permeability for tight oil accumulations in the Chang 7 member, southeastern Shaanbei Slope, Ordos Basin were determined. The results show that the lower limit values of porosity and permeability of effective reservoir are 5% and 0.038×10-3μm2. The critical accumulation periods are mainly the mid-late stage of Early Cretaceous. The physical properties of Chang 7 member reservoir are different between the critical accumulation period and nowadays, and the average differences of porosity between the two ages in the Ⅳa, Ⅳb and Ⅴ reservoir type are 5.15%, 3.46%, 2.32%, respectively. The physical property values of Ⅳb and Ⅴ reservoir type are nearly the current lower limit value of effective reservoir, the average differences of porosity of the two reservoir type between the critical accumulation period and nowadays are 2.79%, and then the lower limit value of porosity and permeability of oil accumulations of Chang 7 member in the study area are 7.79% and 0.10×10-3μm2. [ABSTRACT FROM AUTHOR]