A process for preparing a composite coating of hydroxyapatite and porous titanium dioxide on the biomedical titanium metal surface belongs to the technical field of metal surface modification. Compared with other technologies of coating titanium surface bioactive coating, the process prepares the a composite coating of hydroxyapatite and porous titanium dioxide on the biomedical titanium matrix surface in situ, thereby the adhesion of titanium matrix substitutes implanted into the body and bone tissues is remarkably improved. The process includes the following steps of, firstly, placing titanium or titanium alloy into a stainless steel groove containing an alkaline electrolyte, using a bipolar impulsing power source, controlling micro-arc oxidation electrical parameters and micro-arc oxidation time, enabling the titanium surface to form a porous titanium dioxide coating by a disruptive discharge of the titanium surface; secondly, putting the coating into a reactor containing liquid through a hydro-thermal method, thereby the hydroxyapatite can grow in situ of the biomedical titanium matrix surface in situ. The process for preparing a composite coating of hydroxyapatite and porous titanium dioxide on the biomedical titanium metal surface is simple in operation, high in controllability and low in manufacturing cost, and can introduce non-toxic substances into the coating.