Abstract: The interpretations for the data of crustal depth measurement section of Lisnyun harbor-Linyi-Sishui which is across the mid-section of the fossil Tanlu rift valley in the east of China vary with interpretative methods (Fig. 1). The authors (1983) made an interpretation by one-dimensional vertical heterogeneous crustal velocity model and based on the comprehensive analysis of zeophysical data of gravity magnetic field etc. the authors studied the deep structural background of Linyi 8.5 earthguake. In this paper, baseed onthe above work, by dynamic ray tracing method, the crustal structrual characteristics of the mid-section of the fossil Tanlu rift valley have been further studied with two-dimensional heterogeous velocity model, and a preliminary study of fossil rift valleys formation and its dynamic evolution process has been made.