The invention belongs to the technical field of smelting, and mainly relates to a method for smelting martensitic stainless steel P91 for a boiler pipe. The technological process of an electric arc furnace / medium-frequency induction furnace, an argon-oxygen refining furnace, an LF refining furnace, vacuum degassing, LF and continuous casting is adopted. Components for smelting the martensitic stainless steel for the boiler pipe comprise, by mass percent, 0.08%-0.12% of C, 0.30%-0.50% of Si, 0.30%-0.60% of Mn, not larger than 0.015% of P, not larger than 0.010% of S, not larger than 0.40% of Ni, 8.5%-9.5% of Cr, 0.90%-1.10% of Mo, 0.18%-0.30% of V, not larger than 0.30% of Cu, 0.03%-0.07% of N, 0.05%-0.10% of Nb, not larger than 0.020% of Al, not larger than 0.015% of [As], not larger than 0.010% of [Sn], not larger than 0.010% of [Pb], not larger than 0.010% of [Sb], not larger than 0.010% of [Bi] and the balance Fe and a small quantity of other elements. The method for smelting the martensitic stainless steel P91 for the boiler pipe aims to be low in inclusion content and delta-ferrite content and capable of achieving continuous casting production.