Abstract: The PL oilfield is the first large granitic buried hill oilfield discovered in China. It is characterized by lithological diversity and porous fractured reservoirs. Study of the lithology of the reservoir, therefore, remains critical, even it is quite difficult. Upon the mineralogy and well logging data, a double structure of buried hill consisting of Proterozoic metamorphic rocks and Mesozoic igneous rocks respectively has been recognized. As for the igneous rocks, according to the element composition of the rocks and following the QAPF lithology classification, granodiorite and monzogranite are identified. In combination with well logging data, quantitative discriminant criteria for buried hill igneous rocks are established for the first time. On this basis, the lithology variation is carefully studied, which found the basis for the construction of the buried hill evolution model. In addition, the variation in buried hill lithology and the influence of lithology on the development of buried hill reservoirs are thoroughly discussed. The study results is believed useful in the further research and development of buried hill reservoirs.