Understanding the structure of the pore throat is an important task for tight reservoir development. The common methods of studying the pore-throat structure include pressure-controlled mercury injection (PMI), rate-controlled mercury injection (RMI), X-ray computer tomography (CT), and scanning electron microscopy. We have used those four methods to understand the pore-throat structures of three main lithologies in the Lucaogou Formation, Jimsar Sag, China. The PMI results revealed that the pore-throat size of all of the lithologies ranges from 0.013 to . The RMI testing indicates that the different lithologies within the Lucaogou Formation illustrate a similar pore structure but a different throat structure. The testing of PMI, RMI, and CT together indicated that the size of the throat is the main factor affecting the permeability. The experiments’ results indicated that the pore-throat structures of the tuffaceous siltstone, dolomitic siltstone, and silty dolomicrite are better than those of the other lithologies.