The invention relates to a processing technique of a glass-fiber-reinforced crosslinked polystyrene board, which comprises the following steps: 1) dissolution of polystyrene powder: pouring polystyrene powder into a styrene-divinylbenzene mixed solution, and stirring to obtain a transparent solution; 2) addition of glass fibers: adding long glass fibers treated by a silane coupling agent into the transparent solution, and mixing uniformly; 3) formation of glass-fiber-reinforced crosslinked polystyrene board; pouring the mixture into a mold, sealing, and carrying out radiation by gamma-rays until the liquid solidifies and has certain strength; and 4) later treatment of glass-fiber-reinforced crosslinked polystyrene board: carrying out autoclaving treatment on the plastic board to obtain the glass-fiber-reinforced crosslinked polystyrene board. The autoclaving treatment is carried out to eliminate the gap which can possibly appear on the glass fiber/high polymer interface in the material system, so that the residual small molecules in the system can react completely, thereby further enhancing certain strength of the material.