In recent years, commercial oils have been exploited in the Paleozoic carbonate basement rock of the northwest Song Hong basin. This is one of objects that are paid more attention by oil companies in oil exploration and exploitation. However, the carbonate basement rock in the area has not still been studied thoroughly in terms of petrographic characteristics and post-depositional alteration. Hence, the article focuses on revealing the detailed petrographic component to determine the lithofacies and diagenetic evolution. In the northeast of the study area, the carbonate basement rock is composed mainly of crystalline limestone, packstone, wackestone, and mudstone, and they are rarely dolomitized. In the northwest of the study area, the major compositions of rock are crystalline limestone and packstone. These rocks have been strongly dolomitized forming dolostone that interbeds in the carbonate mass due to the influence of volcanic activities. The carbonate basement mass has been experienced squeezing and dissolution, which produces stylolite texture, fractured pores, vuggy pores and pores in dolomite crystals. According to the petrographic analytic results and presence of foraminiferal assemblages, the carbonate basement rock has been accumulated in the shallow depositional environment.