Effects of hydrogen on the interfacial reaction between Ti-6A1-4V (Ti64) alloy melt and Al2O3 ceramic shell were studied by arc-melting in H-2/Ar gaseous mixture. The thickness of interfacial reaction layer between Ti64 alloy melt and Al2O3 ceramic shell without hydrogenation is 80 gm. But the thickness of reaction layer can be reduced to 10 gm at a hydrogen partial pressure of 20 kPa, which is better than the thickness of interface layer between Ti64 alloy and widely used Y2O3 shells. At Ti64 casting surface, the content of p-soft ductile phase is increased and the width of both reaction zone and transition zone are reduced with the increase of hydrogen partial pressure, thus reduces the hardness and the element diffusion distance. Therefore, Hydrogen can effectively control the interfacial reaction in the process of titanium alloy investment casting, and Al2O3 ceramic will be a kind of very promising shell material. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.