Eocene lacustrine strata are the main source rocks in the field of crude oil exploration in the Qiongdongnan Basin. Over the years, the results of various rounds of resource evaluation show that they have good prospects for oil exploration. However, since the oil layer was first drilled in the Well Ying9 in 1987, no major breakthrough has been made in the field of crude oil exploration in the Qiongdongnan Basin. In recent years, the drilling failure of the Well S3X, which has high hopes, is typical. Taking the post drilling analysis of the Well S3X as an opportunity, this paper puts forward a different view from the past through the comparative study with the Eocene strata of the Pearl River Mouth Basin and the Beibu Gulf Basin. The analysis shows that the content of C304 methylsterane from lower aquatic organisms and the Pr/Ph parameter reflecting redox conditions in the crude oil found in the Qiongdongnan Basin are weaker than those of semi deep lacustrine high- quality source rocks in the Pearl River Estuary and Beibu Gulf Basin; the characteristics of “low frequency continuous strong amplitude” seismic facies in the Qiongdongnan Basin are quite different from those of semi deep lacustrine high- quality source rocks confirmed by drilling in the Pearl River Estuary and the Beibu Gulf Basin; The Qiongdongnan Basin is also significantly different from the Pearl River Estuary and the Beibu Gulf Basin in terms of regional location, structural evolution and sedimentary filling mode, which makes it objectively inferior to the Pearl River Estuary and the Beibu Gulf Basin in terms of the scale of Eocene lacustrine strata and the development conditions of high- quality source rocks. Therefore, it is suggested that we should be prudent in the process of comparative study with Eocene strata in surrounding basins, especially in the study of distribution scale of Eocene lacustrine source rocks in the central depression belt represented by the Lingshui Depression. At the same time, it is pointed out that due to the influence of the geomorphic pattern, the transgression processes of different depressions are not synchronized. In addition to the lacustrine facies strata developed in Eocene, some depressions in the early Oligocene Yacheng Formation also have the conditions for the development of lacustrine facies strata and oil- type source rocks. This new viewpoint can expand the situation and thinking of crude oil exploration and research in the Qiongdongnan Basin to a certain extent.