The utility model provides a combined working platform for internal final assembly of a tail section of a carrier rocket. The device comprises a bottom frame, a lifting mechanism capable of ascendingand descending is connected to the bottom frame, a bottom frame rod is detachably connected to the top end of the lifting mechanism, a bottom-layer working platform and a movable frame are detachablyconnected to the bottom frame rod, an auxiliary platform is connected to the top of the movable frame, and a movable high-layer working platform is connected to the auxiliary platform. The underframeis arranged outside the tail section rocket body of the carrier rocket, and the working platform is arranged inside the tail section rocket body, so that damage to the rocket body due to the fact thatthe whole structure of the working platform enters the tail section is avoided; the working platform is designed in a modular manner, and can be quickly assembled and built during use, so that the working efficiency is improved; the double-layer working platform meets the requirements for different working heights in the rocket body, and the application range of the working platform is widened.