Microstructure performance in the welding zone of T91 heat-resistan stell under the condition of TIG welding was researched by maean of metallography, X-ray diffraction and scanning electron microscope (SME). Experimental results indicated that microstructure of T91 weld metal was austenite+a little amount of 6 ferrite when using TGS-9cb filler wire. Substructure inside the austenite grain was crypto-crystal lath martensite, on which some Cr23C6 blocky carbides were distributed. The maximum hardness (HRC44) in the welding zone is near the fusion zone. There existed no obvioussoftening zone in the heat-affected zone (HAZ). For T91 Steel tube of 63mm