Sigma phase as intermetallic compound with Cr and Mo will increase the strength of steel and make the plastic, toughness and corrosion resistance worse. The precipitation of sigma phase in S31803 and S32750 duplex stainless steel is studied through composition, microstructure, properties and other aspects of in this paper. The results show that Cr and Mo increase the sensitivity of sigma phase precipitation and sigma phase will increase with aging time. Also the sigma phase precipitation adversely affects the plastic, corrosion resistance of the material.