Wuerxun Sag is a Mesozoic fault basin experienced multi-phase superimposition and tectonic activities, where the interaction between the construction and reform has formed strata and erosion. Through the analyses of seismic profiles, five kinds of the construction modes ( single fault type, single fault bench type, single fault trough type, faulted and non-faulted type fault sags ) and three kinds of reform modes ( slip type, rotary type, uplift type ) have been established. On the basis of the control points by single-well interval transit time restoring method and the denudation modes on the seismic profiles, the planar denudation amount is souhgt with the help of formation thickness trend method. The results show the denuded thickness and range in each oil group of Nantun Formation in the sag gradually increase from bottom to top, the denuded axis migrates from the east to the west, and at present Nantun Formation petroleum reservoirs possess much better matching relations with the synchronous palaeostructure developed.