The invention relates to a light rigid plate and a manufacturing method thereof, and belongs to the technical field of composite materials and novel chemical building materials. The light rigid plateis composed of a core layer, a middle layer and an outer shell layer, wherein the middle layer is located between the core layer and the outer shell layer, the core layer, the middle layer and the outer shell layer are independently extruded by three extruders to form a core layer material flow, a middle layer material flow and an outer shell layer material flow respectively, the core layer material flow, the middle layer material flow and the outer shell layer material flow converge in a die to form a mixed material flow, and the mixed material flow is extruded in the die to obtain the lightrigid plate. According to the invention, the light rigid plate is convenient to produce and manufacture, high in production continuity, high in production efficiency, light in weight, high in rigidity, high in strength, not prone to deformation, resistant to flame, water and corrosion, resistant to worm damage, free of cracking and aging, free of color difference, free of paint falling in the using process, free of moisture absorption and moisture regaining and the like.