Abstract: The oxide skin morphology and differences of oxide skin thickness, oxygen rich layer and hardened layer thickness between TA1 pure titanium and TC4 titanium alloy plates were analyzed, and the reasons for the differences were discussed. It is found that the loose and porous oxide skin structure of TC4 promotes oxygen mass transfer and accelerates oxidation, resulting in thicker oxide skin of TC4 than that of TA1. The thickness of oxygen rich layer of TA1 and TC4 is 5 μm and 60 μm respectively,and the porous structure of the oxide skin of TC4 titanium alloy plate is conducive to oxygen mass transfer, which makes TC4 have a thicker oxygen rich layer than TA1. The thickness of the oxygen rich layer is basically the same as that of the hardened layer, and the interstitial solution strengthening effect of oxygen atoms in the oxygen rich layer promotes the formation of the hardened layer.