The sigma phases in tube joints of austenitic heat-resistant steels for power boilers were reviewed. The results show that σ phases with different morphologies were precipi-tated in the austenitic heat-resistant steel joints after high temperature aging. There are two conditions for the formation of the σ phase,one is the composition factor,and the other is the temperature factor. Among the factors influencing the formation of σ phase,the influence of chemical composition is very critical and complex;the amount of σ phase precipitation increases with the increase of aging temperature and time;the excessive heat input has a tendency to promote the precipitation of σ phase.After the sample undergoes high temperature creep,the σ phase with network distribution appears in the HAZ coarse grain region,and the creep fracture strength of the joint is significantly reduced. Optimizing the chemical composition of the weld is the necessary condition to control the formation of σ phase in the weld,and reasonable heat input and its technological measures are the sufficient conditions to control the formation of σ phase in the joints.