To improve the corrosion resistance of biomedical titanium alloys, Ta-modified layer was prepared on Ti6Al4V substrate by double-glow plasma surface alloying technique (DGPSAT) at 750 degrees C. The effects of alloying time of Ta coating on the microstructure, film cohesion strength, as well as the electrochemical corrosion property had been investigated. Results showed that there were mainly beta-Ta phase formed at 750 degrees C, the crystal grew bigger without phase transition and the layer thickness increases with the prolongation of alloying time. However, the cohesion strength and corrosion resistance of the film increase first and then decrease with the prolonging alloying time. In particular, the sample with alloying time of 30 min maintains the best cohesion strength and corrosion resistance. These are attributed to the following factors: a denser and more homogeneous coating with high cohesion strength formed on the substrate, higher positive E-corr and lower I-corr in phosphate buffered saline (PBS) solution. Both of these accelerate the formation of tantalum oxides protective layers on metal surface and thus maintain the excellent properties.