The invention provides a P91 seamless steel pipe and a method for manufacturing the P91 seamless steel pipe. The method comprises the following steps: smelting a blank: performing smelting, refining, vacuum degassing and round-blank continuous casting on raw materials to obtain the blank; annealing: performing high-temperature diffusion annealing and low-temperature isothermal annealing on the blank; rolling the blank periodically: heating the annealed blank uniformly, hot rolling, perforating, sizing and cooling; and carrying out thermal treatment: heating the blank rolled periodically to 1,040-1,080 DEG C, normalizing, preserving heat, cooling, heating to 750-800 DEG C, performing tempering, preserving heat and cooling to obtain the P91 seamless steel pipe. The content of P in the raw materials is less than or equal to 0.015%, and the content of S content is less than 0.007%. and the diameter phi of the seamless steel pipe is 325-720mm. The P91 seamless steel pipe manufactured by adopting the method is compact in internal structure and excellent in performance. The metal yielding rate and the steel pipe forming yield are improved, the production cost is reduced, and resources are saved.