The invention discloses an aluminium nitride ceramic material and a preparation method thereof. The method is to add nano-alumina to raw materials in the prior preparation method for preparation according to the prior preparation process. In-situ growing nano-alumina can be obtained directly through adding the nano-alumina, or indirectly through adding organic aluminum, such as aluminium secondary butylate, aluminium isopropoxide or aluminium acetylacetonate, and by means of low-temperature decomposition of the organic alumina. The method can be applied to dry pressing and tape casting shaping, can obtain slurry with good dispersing characteristic and even mixing of the aluminium nitride and the nano-alumina by the ceramic preparation process, such as normal pressure, hot pressed sintering or the like, and is favorable for the improvement of sintering activity of materials, the reduction of sintering temperature, the improvement of luster uniformity, planeness and roughness for a ceramic substrate, and the reduction of production cost. The aluminium nitride ceramic material and the preparation method thereof can be widely applied to the field of aluminium nitride ceramic production.