Abstract: Existence of δ ferrite in the steel will not only negatively affect the properties of the steel tube,but also lead to development of both inner and outer folds thereof.Analyzed is the elements that cause the formation of δ ferrite in the P91 hot-rolled seamless steel tube,and influence by such elements on quality of the tube.Based on the analysis,relevant technical proposals are put forward,including optimizing chemical composition of the steel,properly controlling the chemical segregation of the ingot,and the temperature for hot-rolling/piercing process in a bid to prevent formation of δ ferrite in the P91 hot-rolled seamless steel tube.