Constant-rate mercury penetration was used to study the microscopic pore space of tight sandstone reservoir in Shahezi formation of Xujiaweizi depression, and distribution of pore and throat and their control on reservoir physical were analyzed．The results show that the distribution range of pore radius is mostly 100~200 μm and is barely influenced by reservoir physical. The correlation of pore radius and reservoir physical is not significant, thus the pore radius has the secondary control on petrophysical property. Throat radius varies greatly with the reservoir permeability, and the distribution range of throat radius tends to increase with the reservoir permeability. However, the distribution range of throat radius is no more than 5μm in value. Throat radius is correlated with porosity slightly, while it is strongly influenced by permeability, indicating that throat is the main factor that controls reservoir. The porethroat connectivity of sandy conglomerate samples is not well, with pore throat ratio ranging form 20~600. The throat favorable for reservoirs is mainly over 0.5 μm in radius and less than 200 in pore throat ratio.