The invention relates to a memorial hall horizontal inscribed board in situ trimming construction method. In situ restoration of a memorial hall horizontal inscribed board is carried out through cleaning of the horizontal inscribed board and through restoration treatment of horizontal inscribed board gold characters by adopting a gold overlying technology to substitute an original gold decoration technology without taking off the horizontal inscribed board in order to recover the original luster. A movable hydraulic elevating platform is adopted during construction, the elevating platform is moved to the corner and does not affect look with reverence when the memorial hall is open, and construction is continued after the look with reverence, so the restoration effect of the horizontal inscribed board is reached, no influences of the construction on publics' look at the memorial hall horizontal inscribed board with reverence is guaranteed, the stereo image of the memorial hall is not destroyed, and the influence is maximally reduced. The method omits construction of dismounting of the high and large horizontal inscribed board of the memorial hall, reduces the construction difficulty, guarantees the construction efficiency and the construction quality, and can be widely applied in the in situ restoration of the horizontal inscribed board.