The invention relates to the field of 
surface modification of biomedical materials, in particular to a biological active 
coating on the surface of 
titanium or a 
titanium alloy and a preparation method thereof. The 
coating is a composite gradient 
coating; the inner layer is a 
titanium oxide film layer with the thickness between 0.5 and 10 mu m; the intermediate layer is a 
sodium titanate gel film layer with the thickness between 0.1 and 10 mu m; and the outer layer is a 
hydroxylapatite layer with the thickness between 1 and 15 mu m. A method combining anodization and alkali treatment is adopted to prepare the biological active coating on the surface of the titanium or the 
titanium alloy, which comprises the following steps: firstly, preparing an 
oxide film with certain thickness on the surface of the titanium or the 
titanium alloy by an anodization method; secondly, forming a layer of porous netty 
sodium titanate gel film layer on the surface of the 
oxide film by an alkali treatment method; and finally, depositing the bone-like 
hydroxylapatite layer on the surface of a sample after the treatments in a 
simulated body fluid. The method can effectively improve the 
biological activity on the surface of the titanium or the 
titanium alloy; and the surface has a coarse porous structure, so the bonding force of the 
hydroxylapatite layer and the 
adhesive ability of cells are improved.