Abstract: The tectonic subsidence of Subei basin ceased during Sanduo movement from Late Eocene to Oligocene. It had broughtabout the end of faulting growth in it and depositional break for 18Ma, with strong uplifting,erosion and absence of UpperEocene and Oligocene. The imbalanced erosion of Gaoyou sag is analyzed by the data of homogeneous temperature, clay mineral,vitrinite reflectance and C29-20S/(20S+20R) sterane ratio. It is shown that the erosion becomes stronger gradually from deep sagzone to slope zone,fault terrace zone and low uplift. The erosion thickness is estimated by the method of interval transit timeand forward numerical simulation of vitrinite reflectance. The results of them coincide with each other. The total erosion thicknessis about 400~1 600 m, where deep sag zone is of 400~600 m, slope zone of 500~1 200 m, fault terrace zone and low uplift of1 000~1 600 m in total. Such estimated values are bigger than previous results of qualitative estimation, which mean that renewalstudies should be made in the burial history, geothermal history, hydrocarbon accumulation history and oil-gas reservoir distributionn Gaoyou sag.

Key words: Subei basin, Gaoyou sag, Eocene, interval transit time, vitrinite reflectance, erosion thickness