<p>Pore structure is a key factor affecting fluid mobility and hydrocarbon production in tight sandstone reservoirs. In this study, a fine division of lithofacies was carried out for the tight sandstone of the fourth member (Mbr 4) of the Xujiahe Formation. The diagenetic evolution characteristics of each lithofacies and their influence on the pore structure of the reservoir were analyzed. The results showed that the tight sandstone of the Mbr 4 can be divided into three lithofacies: massive or bedding medium sandstone (MS), argillaceous laminae fine–medium sandstone (AMS) and carbonate-cemented fine–medium sandstone (CMS). The MS lithofacies had coarse grain size, good sorting and less cement content. The clay minerals were mainly grain-coated chlorite, which can protect the primary pores. The strong dissolution produced a large number of feldspar dissolution pores, so the lithofacies has better pores space and fluid mobility. The AMS lithofacies had finer grains and more argillaceous laminae, which can lead to greater damage to the primary pores of the reservoir by compaction and hinder the activity of pore fluid, resulting in a lower degree of dissolution. The clay minerals were mainly illite and illite–smectite mixed layers, which can fill part of the pore space, resulting in poor reservoir pore structure and fluid mobility. In the CMS lithofacies, the compaction had little damage to the pores, and the densification of the reservoir was mainly caused by cementation. The carbonate cements were difficult to dissolve, resulting in almost no development of primary pores in the reservoir, and the reservoir quality and pore structure were the worst.</p>