Overhead analysis was developed as a performance tuning approach for parallel programming and were adopted by several performance analysis systems for OpenMP programs. In this paper, an extended overhead analysis scheme based on layered model is proposed for OpenMP programming, to further enhance the capability of overhead analysis and thus make the OpenMP performance tuning easier. An example case called ILP/TLP overlap is studied in detail to show the idea of layered overhead model, and a new way to organize the overhead hierarchically is also presented based on the layered overhead model.