We obtain a high-resolution velocity structure of the upper mantle in the Ordos block and its surrounding regions by travel-time tomography, using the teleseismic P-wave data recorded by dense temporary stations of China Seismic Array and permanent stations. The results show a thick high-velocity anomaly beneath the Ordos block, which extends to a depth of about 180 km in the west, 150 km in the north, and up to 300 km in part of the central area, indicating that the Ordos block still maintains craton stability as a whole. The relatively thin lithosphere in the northern Ordos may be related to the heating and modification of the lithosphere by the mantle upwelling, whereas the lithosphere thinning in the western Ordos may be associated with the lateral expansion of the warm upper mantle of northeastern Tibet. The upper mantle of the eastern North China Craton, the central North China Craton and the northeastern Ordos block exhibit broad low-velocity anomalies, which may be related to an extensional tectonic setting caused by the rollback of Pacific Plate, the dehydration of the stagnant slab and the local convection at the front edge of the slab. In extensional environments, melts from the lithosphere or asthenosphere upwelled along the weak zone and formed volcanoes including Datong volcano.