Abstract: By a revolving flexible copper electrode, titanium alloy surface was strengthening treated in air. The strengthening layer was researched by SEM, XRD, hardness tester and surface roughness tester. The results show that the titanium alloy strengthened layer consisted of oxides (TiO, etc) and intermetallic compounds (CuTi, Zn2TiO4, Cu4Ti3, etc). The thickness of the strengthened layer was 13-110 μm and increased with increasing the current density. Grains in the strengthened layer were refined and even nano-crystalline formed. Compared to the matrix hardness the surface hardness increased by 195% to 266%, and increased with increasing the discharge energy density. Surface strengthening treatment had little effect on surface roughness of the titanium alloy.