The invention discloses a rectangular staggered joint shield based capping segment and post segment assembling structure and method. The method comprises steps as follows: lower T-shaped segments at the bottom of assembling space as well as left waist segments and right waist segments located on two sides of each lower T-shaped segment respectively are assembled; a first assembling zone is reserved at the top of the assembling space; a second assembling zone is reserved on the left side or the right side of the top of the assembling space; upper T-shaped segments are assembled in the first assembling zone; capping segments are assembled in the second assembling zone; post segments are assembled between the upper T-shaped segments and the lower T-shaped segments. The upper T-shaped segments, the capping segments and the post segments are sequentially mounted, and the capping segments and the abutted waist segments are not staggered, the ring height difference between adjacent rings and an assembling gap between the adjacent segments are effectively controlled, the problem that the capping segments cannot be inserted into the gaps is solved, a gap between the upper and lower T-shaped segments is easier to control, and the longitudinal insertion stability of the middle post segments is high.