The invention relates to a total-pressure-design main steam system which is composed of a steam generator 1, a steam generator heat transfer pipe 2, a main steam isolating valve 3, a super pipeline 4, a steam turbine 5 and a steam pipeline 6, wherein the steam generator 1 is positioned in a containment vessel; the main steam isolating valve 3 and steam turbine 5 are positioned outside the containment vessel; the steam generator heat transfer pipe 2 is positioned in the steam generator 1; one end of the super pipeline 4 is connected with the steam generator 1, and the other end is connected with the main steam isolating valve 3; the super pipeline 4 adopts the total pressure design; the steam generator 1, main steam isolating valve 3 and super pipeline 4 can bear the pressure equivalent to the reactor coolant system; and the main steam isolating valve 3 is connected with the steam turbine 5 through the steam pipeline 6.