Effect of different TA15 powder additions on high temperature oxidation kinetics of pre-laid laser melting 45CrNiMoY alloy steel was studied. Thermogravimetric method was used to determine the kinetics curve of constant temperature oxidation of alloy steel sample at 700℃. The results show that bainite and acicular ferrite are the main microstructures of alloy steel after adding TA15 powder. With the increase of TA15 powder, the microstructures showed a distinct trend of refinement. The oxidation kinetics curves of alloy steels follow the linear law. The alloy steels with 1.0 wt.% TA15 powder have the best resistance to high temperature oxidation, and the oxidation rate constant is 1.48×10-4 mg2·cm-4·h-1. Particle reinforcement phase formed in alloy steel can provide pinning effect for oxide film, while micro-cracks added in excess TA15 alloy steel sample are not conducive to the improvement of high temperature oxidation resistance.