Abstract: In the light of more and more titanium alloy material being used to produce important components of spacecrafts and problems existing in traditional jointing process,a fully shielded welding equipment has been developed.The protection reliability is greatly relative to purity of inert gas in welding chamber.While using the economic and effective way by increasing the gas pressure of the welding chamber,which is used to maintain the purity of the inert gas,the chamber pressure becomes the focus to which we must pay attention.This paper analyses the behavior of inert gas pressure in the fully shielded welding chamber,the influences produced by welding operations upon the pressure of inert gas in the welding chamber are discussed,the measures which should be adopted to avoid conta minating the shielded environment in the welding chamber are pointed out.