Abstract: Uner the condition of tungsten-inert-gas (TIG) welding+shielded metal arc welding (SMAW) technology,the microstructure in the welding zone of P91 heat-resisant steel is researched by means of SEM,X-ray diffractometry (XRD) and TEM.The size of the test piece is φ234 mm×26 mm.The test results indicate that when the heat input (E) of TIG welding is 8.5~11.7 kJ/cm and the heat input of SMAW is 13.3~21.0 kJ/cm,the microstructure in the weld metal is composed of austenite and a little amount of ferrite.The sub-structure of austenite is crypto-crystal lath martensite,which has included regular angle.There were some spot precipitates in the martensite base which was confirmed by TEM analysis.There are some carbide (lattice constant is 1.064 nm) at the boundary of grain and inside the grain,most of which is Cr₂₃C₆.