震源深度是描述震源信息的基本参数之一，也是目前最难测准的参数之一。近震深度震相sPn与Pn震相到时差与震中距无关，是测定地壳内地震震源深度的主要依据之一。sPn与Pn到时差测定地壳内近震深度的方法简洁、准确，可以在日常地震速报中应用。

 Depth of focus is a very important earthquake parameter. In this article the preliminary exploration to the determination of focal depth of near earthquake by means of the arrival time difference between the sPn and Pn phases. This method is simple，quick and accurate. The sPn is of great significance for our study to determine focal depth of the within-crust earthquakes that the arrival time difference between sPn and Pn is independent of epicentral distance. This method of analysis and determination is simple and accurate，so it can be extend to the regional earthquake analyzing in the seismic network daily work.