Abstract: Based on the data of regional geological surveying and mapping in a scale of 1:50000 in Beipiao-Yixian district, Western Liaoning Province, the features of sedimentary environment are analyzed for the bird fossil-bearing beds in Sihetun area. They are as follows:(1)Horizontal beddings are widely developed in the sediment of mainly mudstone and fine-clastic rocks, with volcanic fragmental products.(2)The fossil-bearing beds can be vertically divided into three fossil assemblages,of which the middle assemblage contains fossil birds.(3)Due to the effects of volcanic activity, there exists at least three times of volcanic earthquakes.(4)The significant changes of lake surface level took place three times. The volcanic activities caused catastrophic biological death. (5) The anomalous δEu and δCe of REE and the anomaly of trace elements indicate the environmental change of the paleobasin and its influence on living nature. To sum up, the earth environmental changes provided evidence for the evolutive period and qualitative change of the Jehol Biota represented by precious fossils.