This paper presents a review on the definitions, research status and commonly-used research methods in paleolimnology, and takes the Paleogene oil shale bearing lake in Huadian basin, Jilin Province, as a case study. According to the vertical variations of TOC content, the authors interpret that the paleoproductivity of Huadian Basin varies as Middle Member(oil-bearing)＞ Upper Member(coal-bearing)＞ Lower Member (pyrite-bearing). Such a variation indicates that paleoproductivity was the highest when the oil shale was forming. From the petrography and mineral features of oil shale, the ratios of V/V+N, Sr/Ba and B/Ga, the authors conclude that the paleo-water characterizes as alternatively variation of fresh to brackish-saline water.