The invention relates to a crystallized modified polystyrene board and a manufacturing method thereof. The crystallized modified polystyrene board is high in compression strength, low in heat conductivity coefficient, high in flame retardation and good in heat preservation effect. Crystallized modified micro powder is composed of 50%-60% of calcined kaolin, 20%-30% of sea-foam stone powder, 5%-10% of grading micro powder, 10%-20% of crystallized modified emulsion and the like. All the raw materials are stirred into slurry, the slurry is made to permeate into the polystyrene board through negative-pressure permeation, the surfaces of polyphenyl particles are wrapped by inorganic fireproof materials, and thus the crystallized modified polystyrene board reaches the A-grade non-combustible combustion performance. The density of the crystallized modified polystyrene board is 80-160 kg/m<3>, the compression strength of the crystallized modified polystyrene board is 0.2-0.4 MPa, the heat conductivity coefficient of the crystallized modified polystyrene board is smaller than or equal to 0.04 W/(m*K), the PH value of the crystallized modified polystyrene board is neutral, and the combustion performance of the crystallized modified polystyrene board can reach A2(s1,d0,t1); the physical performance, the heat preservation performance and the fireproof performance of the crystallized modified polystyrene board are well combined, both the requirement for energy saving of a building and the requirement for safety of the building are met, and great social benefits and economical benefits can be generated.