The invention discloses a thermosetting molding polystyrene board and a production process thereof. The thermosetting molding polystyrene board comprises the following components: polystyrene particles, cement, glass fibers, fine sand, coarse whiting, fly ash, a flame retardant, an interface agent and water. The production process of the thermosetting molding polystyrene board comprises the following steps of (1) uniformly mixing and stirring polystyrene particles, cement, glass fibers, fine sand, an anti-cracking agent, fly ash, a flame retardant and water to obtain a mixture A, (2) adding aninterface agent into the mixture A, and uniformly mixing and stirring under a heating condition to obtain a mixed solution B, and (3) pouring the mixed solution B into a mold for molding to obtain the thermosetting molding polystyrene board. The cement, the glass fibers, the fine sand, the anti-cracking agent, the coal ash and the flame retardant are added into the polyphenyl particles through stirring under the heating condition, the phenomena that a traditional building external wall panel is inflammable, low in structural strength and prone to falling off are overcome, and the strength andflame retardance of the produced polyphenyl board are remarkably improved.