Southern Alaska is one of the most seismically active regions in north America as the Pacific plate subducts northward beneath North America plate along the Aleutian trench. In this study, we determine P- and S-wave speed and Possion's ratio (Vp/Vs) of the southern Alaska subduction zone based on broadband tele-seismic data recorded by 198 seismic stations for about 2000 events with magnitudes greater than 5.5 during the period from June 2000 to December 2014.  Arrival times of P and S phases are accurately measured by adapting the efficient multi-channel cross-correlation (MCCC) technique. With a wavelet-based multi-scale model parameterization, we map the 3D Vp and Vs 3-D structures based on a finite-frequency tomographic technique. Our tomographic results show strong positive velocity anomalies in the crust and upper mantle starting at depth about 50km extending to northwest to a depth of 200km and covering about 350km in horizontal distance. The high velocity slab has a thickness of about 50km and a subducting angle of about 45 ^o , consistent with some previous studies of southern Alaska.