Non-isothermal oxidation behavior of Ti-Al-Mo titanium alloy’s high temperature weld metal after molten pool solidified during cooling process at different temperatures in the range of 500~1300℃ was studied, and the oxidation mechanism in air and CO2 atmosphere was compared and analyzed. The surface oxidation degree of the sample, the morphology and phase of the oxide layer were studied by means of oxidation weight gain method, XRD, SEM and XPS. The results show that the oxidation degree of the sample in CO2 atmosphere is lower than that in air atmosphere, and the oxide particle size of the oxide layer in CO2 atmosphere is smaller and more compact. The main phase of oxide layer in both atmospheres is rutile TiO2. Besides, the mixed oxide of (TiO2+Al2O3) is observed in the surfacial layer, and the proportion of Al2O3 in CO2 atmosphere is higher. The oxide layer porosity in CO2 atmosphere is lower , which reduces the internal matrix diffusion of CO2. And the reaction thermodynamics inclination of the titanium alloy with CO2 is significantly lower than that with the air, so titanium alloy weld metal in the environment of CO2 atmosphere will have lower oxidation tendency. It’s proved that CO2 can be used as a protective gas in a certain temperature range during the cooling process of titanium alloy weld metal.