The crustal and upper mantle structure of Kunlun-Chaidamu-Qinling-Dabie tectonic zone is studied by using the data available from Chinese Digital Seismographic Network. The average thickness of sedimentary layer is about 8km with a shear wave velocity of 2.62km/s. It is noted that average velocity of 3.50km/s in the crust is relatively low, and there exists a low velocity layer in the lower crust. The undulation of the crustal thickness from East to West China is not great, being about 48km thick on average. The low velocity layer in the upper mantle appears at the depths of 70 to 90km. Such tectonic feature is different from both platform and the Tibetan plateau. Being a transition tectonic zone among geological blocks, it is indeed an independent tectonic unit of the crust in China.