Experiments indicate that the size and shape of the final focal spot are mostly dictated by phase noise added to the beam. To diminish the static phase aberrations of large aperture lasers and promote the concentration degree of focal spot, phase corrector plate is proposed. For the technical integration line (TIL) being built in China Academy of Engineering Physics (CAEP), phase aberration of the main amplifier is the largest contributor. Considering peak fluence of the inserting places and the machining process of the phase plate, four potential locations are evaluated, and the cavity mirror is chosen to be the preferred place and is replaced by the phase plate. Numerical calculation model is established to design the corrector plate. Cut-off frequency of the glass-slab filter is discussed and 0.01 mm-1 is optimally chosen for the lowpass filter. The surface shape and the machining technique of the phase plate are given. Using SG99 light propagation code, simulations demonstrate that the corrector plate can effectively compensate optic finishing errors, and static phase aberration is decreased from 3.35λ to 1.27λ. Further more, times diffraction limit (TDL) containing 95% energy of focal spot is improved from 6.21 to 3.95.