Abstract: The probability and the main effect factors of isothermal superplastic diffusion bonding of W6Mo5Cr4V2/45 steel were examined.Microstructure and strength of welded joint as well as change of microhardness were observed and analysed by means of SEM (scanning electron microscope) and microhardness test.Results showed that after fine-graining treatment and short time (at 3~5min) superplastic pressing formation under the conditions of superplastic temperature (at 750~780℃),pre pressing(80~100MPa) and a strain rate(1.0~3.0×10^-4s^-1),W6Mo5Cr4V2/45 specimens could achieve solid-state diffusion bonding and the property of welded area was the same as the other parts in the specimen.