Abstract: The Milankovitch Astronomical Cycles were applied to study the erosion thickness of Qingshankou Formation (K₂qn) in the X Oilfield, Songliao Basin. Spectral analysis and wavelet transform revealed that the Milankovitch Cycles occurred in the K₂qn. We detected the eccentricity period of 100 ka, obliquity period of 40 ka and precession period of 20 ka in the K₂qn. The bandpass filtering of 42 exploratory wells in the X Oilfield showed that, the K₂qn has 35 to 43 eccentricity periods of 100 ka, which proved erosion phenomenon. The erosion thickness of K₂qn is 0-98 m, and gradually decreases from northeast to southwest, where non-denuded areas distribute widely. Tectonic uplift and erosion took place regionally in the X Oilfield during or at the end of the sedimentation of K₂qn.