An M_S6.5 earthquake occurred in Ludian,Yunnan Province on August 3,2014,and caused heavy casualties and property losses. The seismogenic structure of Ludian M_S6.5 earthquake was quite complex,and had attracted wide attention of seismologists. In this paper,a 3D layered heterogeneous velocity model in Ludian area is established based on a 3D modeling method,and a segmentally iterative ray tracing method is used in the traveltime calculation of Ludian M_S6.5 earthquake. We utilize the first arrivals recorded by the regional stations within 150km of epicenter distance,and calculate the focal depth of Ludian M_S6.5 earthquake through the method of traveltime fitting. The focal depth of Ludian M_S6.5 earthquake obtained in this study is about 12km,which is close to the results of previous studies. Numerical tests indicate the effectiveness of our methods of blocked modeling and ray tracing.