The invention discloses an aluminium nitride ceramic substrate, and a preparation method thereof. The aluminium nitride ceramic substrate is prepared from an aluminium nitride ceramic tape casting slurry. The aluminium nitride ceramic tape casting slurry comprises aluminium nitride powder, a sintering air, a dispersant, a solvent, a plasticizer, a binder, and a defoaming agent. The preparation method comprises following steps: 1, primary ball milling is carried out; 2, secondary ball milling is carried out; 3, vacuum defoaming is carried out; 4, an obtained mixed slurry obtained via step 3 is subjected to tape casting, is subjected to heating on a film band, is cooled naturally, and is peeled off from the film band so as to obtain aluminium nitride tape casting sheets; 5, the aluminium nitride tape casting sheets are overlapped so as to obtain an aluminium nitride green body; 6, additive removing is carried out so as to obtain an aluminium nitride blank; and 7, sintering is carried out so as to obtain aluminium nitride ceramic. According to the preparation method, aluminium nitride is obtained via tape casting of a benzene-free, ketone-free, nontoxic organic solvent, and the sintering aid is added, so that the aluminium nitride ceramic substrate can be obtained via sintering at a relatively low temperature.