The activity of a cratonic block during its evolution is the key in studying the continental preservation. Cratonic block reactivation of diverse scales is in close relation to mineral deposits such as oil， gas， coal， uranium and salt， and controls the intra-plate earthquake activity， thus has been one of the hot topics in the field of energy， resource， and environment researches. The Ordos Block located in western North-China craton （NCC）， is taken to reveal its tectonic activities， referring to as “reactivation” in the study. The analysis of deep boreholes and high-resolution reflection seismic profiles， indicates that the reactivation of the Ordos Block can be shown in six aspects as follows. First， five stages of rifting or extension in or around the block occurred during the Mesoproterozoic， the Cambrian to Early Ordovician， the Carboniferous to Early Permian， the Middle to Late Triassic， and the Cenozoic； second， there were six stages of magmatism in the block during the Middle to Late Proterozoic， the Ordovician， the Late Carboniferous， the Middle to Late Triassic， the Early Cretaceous， and the Late Miocene to Quaternary， with the magmatic events coming to peak during the Changchengnian Period and the Early Cretaceous； third， there were seven stages of faulting and development of faulting-related folds； fourth， there are ten regional unconformities developed including the Ch/AnCh， Jx/AnJx， Z/AnZ， C?/AnC?， O/AnO， C/AnC， T/AnT， J/AnJ， K/AnK， and Q/AnQ； fifth， the block underwent four tectonic subsidence cycles of the Middle to Late Proterozoic， the Early Paleozoic， the Carboniferous to the Triassic， and the Jurassic to Cretaceous， with a marked migration of the subsiding centers； and sixth， a number of strong earthquakes occurred along the peripheries and the interior of the Ordos Block with the interior uplifting while the periphery rifting and rapidly subsiding during the Cenozoic. The evolution of the Ordos Block is predominantly controlled by the adjoining plate tectonics and the deep tectonic activities， to some extent with a possible large-scale thinning of the lithosphere in the Early Cretaceous， and also the reactivation and thinning of the lithosphere in northern part of the Ordos Block during the Late Cenozoic， which is resulted from the anti-clockwise rotation of the block， and thus the upward intrusion of the partial molten melts of the upper mantle along the weak zones of the graben systems around. The Ordos Block therefore took typical properties of reactivation， which may have played a profound role in the basin formation， the hydrocarbon generation， and the pool-formation in the block.
