The invention relates to a microwave device ceramic substrate material and a preparation method thereof, and belongs to the technical field of electronic materials. The microwave device ceramic substrate material comprises a main crystal phase and a modified additive, wherein the chemical general formula of the main crystal phase is Mg(1+x)CoyTiO(3+x+y), x is more than 0.01 and less than 0.05, y is more than 0.001 and less than 0.01, the modified additive is one or a plurality of materials selected from CeO2, Nb2O5, Nd2O3, ZnO, MnCO3 and SiO2, and the mass of the modified additive is 0.0-4.0%of the total mass of the whole microwave device ceramic substrate material. The preparation method comprises processes of material preparing, ball milling, pelletizing, forming and sintering. The microwave device ceramic substrate material has characteristics of high Q*f value (80000-100000), medium dielectric constant (17-20) and serialization dielectric constant temperature coefficient (0-110),is applicable for preparations of the microwave device substrate materials, and can meet the preparation requirements of the microwave devices (especially the microstrip filter). The method of the present invention has characteristics of simpleness, easy control, environmental protection and low cost.