Abstract: In order to confirm the appropriate thickness of bearing steel layer diffusion bonding on titanium alloy surface, the elastic modulus of materials was measured by Nano Indenter Ⅱ. Stress distribution and integrated distortion of the titanium alloy which bonded bearing steel layer were analyzed by finite element simulation under press stress, and the thickness of bearing steel layer was optimized and designed. The results show that when the thickness of hardened layer is 0.10-0.50 mm, the maximal equivalent stress is located the interface of titanium alloy and bearing steel layer, which can easily induce interface cracks; the appropriate thickness of bearing steel layer is 1.00-2.00 mm, and the optimal thickness is about 1.50 mm.