The reactivation of craton is a crucial issue for the understanding of continent lithosphere. Although the partial loss of the thick lithospheric root of the North China Craton (NCC) was documented, its mechanism remains a contentious topic in the study of cratonic evolution. In this paper, we imaged the crust-mantle structures by using the data from 36 permanent stations with fine spatial coverage in the Yanshan tectonic belt (YSTB) and the Taihangshan region (TSR) in the northern NCC. Two tectonic units with distinct crust-mantle structures were recognized and their junction zone was identified. The results reveal distinct features of the crust-mantle boundaries of the YSTB and the TSR which are characterized by a sharp interface and a thick transition zone, respectively. Based on the analysis of the seismic structures of the crust-mantle boundary and the upper mantle, we propose that the NCC reactivation was possibly derived by a slow secular ascension of hydrated asthenospheric material atop the stagnant Pacific slab, which influenced the formation of crust-mantle transition zone in the eastern NCC. On the other hand, regional delamination of the deep crust after orogenic thickened and/or magmatic underplating beneath the YSTB caused the spatial variation of the crust-mantle boundary. Both of the mantle processes possibly changed the nature of the lithospheric mantle.