Slurry-phase hydrocracking (SPHC) of unconventional heavy feedstocks is considered as a promising process to fill the gap between the ever-increasing demand for vehicle fuels and the fast-depleting supply of conventional crude oil. The one-through nature of SPHC processes requires low-cost yet high-performance catalyst. This article reports a simple but effective hydrothermal modification strategy to treat a cheap natural bauxite mineral as a support (HMB) to prepare SPHC catalyst (HMBC) with outstanding catalytic performance. For comparison, an acid-modified bauxite (AMB) derived catalyst (AMBC) was also prepared. The physicochemical properties of HMB, HMBC, AMB and AMBC were systematically characterized, and the catalytic performance of HMBC and AMBC was assessed in the SPHC of a high temperature coal tar (HTCT). The results showed that HMBC exhibited HTCT hydrocracking activity superior to AMBC, attributed to the more suitable acidity of the support HMB and the weaker interaction between MoO3 and HMB that results in the higher sulfidation degree of molybdenum oxide species and thereby provides more active MoS2 phases for hydrocracking. Furthermore, compared with the acid treatment previously reported, the hydrothermal modification is simpler, more energy-saving, and more environment-friendly and therefore is feasible for industrial application.