The present disclosure provides a method for preparing a transition metal lithium oxide, comprising steps of: A) mixing a lithium salt and a transition metal compound, and performing a pretreatment to obtain a precursor; wherein the pretreatment temperature is 100-300° C.; and the pretreatment time is 1-10 h; B) precalcining the precursor to obtain an intermediate; and C) continuously feeding the intermediate into a feed port of a moving bed reactor, and calcining, to obtain a transition metal lithium oxide. In the present disclosure, a pretreatment process is performed before the precalcination, and the pretreatment temperature and time are further limited, thereby solving the problem of material hardening during the calcination process of battery materials. In conjunction with using a moving bed reactor, the gas phase and the solid phase are sufficiently contacted, and at the same time the thickness of the filler is increased, the productivity is enhanced and the oxygen consumption is largely decreased at the same time. The present disclosure further provides an apparatus for preparing a transition metal lithium oxide.