The work aims to improve high temperature oxidation resistance of Nb-TiAl alloy. In this paper, Y modified silicide coating was prepared on high Nb-TiAl surface by taking NaF as catalyst and diffusing and co-penetrating Si-Y for 5 h under 1080 ℃. Effects of Y2O3 content in permeating agent on co-deposition coating and its phase composition were analyzed by virtue of XRD, SEM and EDS. All Si-Y coatings prepared with different contents of Y2O3 were provided with a multi-layer composite structure. Thickness of the coatings firstly increased and then decreased with the addition of Y element in the pack. All inlayers of the coatings were mainly composed of a γ-TiAl phase. The outer layers of the coatings prepared at 1080 ℃ for 5 h with the pack mixture containing 2% or 3% Y2O3 were mainly composed of (Ti，Nb)Si2 phase, and the middle layer was divided into upper and lower layers composing of (Ti, X)5Si4 and (Ti, X)5Si3 respectively. Moreover, a superficial layer consisting of Al-rich (Ti,Nb)5Si4 and (Ti,Nb)5Si3 was detected in the coating prepared with 2% Y2O3. However, the constituent phase turned to (Ti, Nb)5Si4 in the out layer and (Ti, X)5Si3 in the middle layer of the co-deposition coating when the pack mixture contained 0%, 1% or 5% Y2O3. The coating growth can be catalyzed obviously when the content of Y2O3 in the pack mixtures ranges between 2%~3%. However, excess addition of rare earth element will restrain the adsorption and diffusion of Si element, and thus a number of holes will appear on Si-Y co-deposition coating and the layer structure will change.