The utility model discloses a steam main pipeline structure for an ultra supercritical unit. The steam main pipeline structure comprises a steam main pipeline and a main pipe drain pipe, wherein the main pipe drain pipe is connected onto the steam main pipeline and is provided with a first drain valve, two steam branch pipelines communicated with a steam machine are connected in parallel onto the steam main pipeline, a branch pipe drain pipe provided with a second drain valve is arranged on the steam branch pipelines, and the two steam branch pipelines are respectively provided with warm pipe steam exhaust pipes provided with steam discharge valves. The steam main pipeline structure has the characteristics that the structure is simple, the pre-warming time is short, and the starting speed is high.