Abstract: Microstructures, precipitation and HAZ fracture morphology in welding joint zone of a new high-purity CrI8Mo2 ferritic stainless steel were researched by means of metallosoope, SEM, TEM and electron diffraction, etc.. Experimental results indicated that crystalline grain coarsing in HAZ still is one of the causes resulting in the embrittlement fracture in welding zone of the ferritic stainless steel. Precipitation (TiC, TiN and Cr₂N, etc.) in the steel has a promoting effect for producing and developing of the brittle cracks. In practical production, the welding heat input (q/v) should be as small as possible to prevent the embrittlement caused from grain coaising in HAZ.