Abstract: An improved method to calculate denuded amount by the exponential model of sonic propagation time vs. depth is suggested in this paper. The method considered the physical range of sonic propagation time in rock matrix and the sonic propagation time in Earth's surface, and can well reflect geologic reality and predict compaction trend in shallow and great depths so as to improve the estimation of denuded amount. The improved method is applied to the Triassic strata of the Xihu Depression, the East China Sea by the authors to fit compaction trend and to calculate the denuded amount of major unconformity planes. The estimated denuded thickness of T₁⁰ interface at the end of the Miocene in well Donghai-1 is about 1750m.