In this work, the construction of hodographs of travelling times of P and S - waves and determination of velocity model of the Earth's crust of Vietnam territory have been first time conducted systematically by using an unified methodology and diversified data sets of travelling times of P and S - waves together with computation program, which have been established by the authors. A family of average travelling velocity hodographs and velocity models of the Earth's crust for both types of P and S-waves in the North, Central and South Vietnam have been constructed. The P and S velocity models of the Earth's crust of central and southern regions showed clearly similarity in both number of layers and boundary depth (Or layer , thickness) in each area, proving the accuracy of the data used as well as the correctness of the models established for these regions. For northern region, both P and S velocity models demonstrated 4-layer media with relatively similar depth of the first layer, H1 ~ 3-5 km
The depth difference was only observed in following layers. This difference may be attributed to the error occurred in the data conversion, incorrect differentiation and determination of the incidence time of the different phases of the S-wave on seismic records. The Earth crust velocity models obtained in this study are not only detail and sufficient, but also suitable for actual conditions of each region and have high reliability. Therefore they can be used in positioning and determining accurately the basic parameters of earthquake foci in Vietnam.