To fully exploit the abundant bioresource crop straw, a straw-based composite with excellent fire retardant, high strength and dimensional stability was successfully prepared for use in building applications. The subject composite was composed of rice straw/magnesium cement (SMC) adhesive, with glass fiber as a reinforcement agent. The mechanical strength, dimensional stability, flame retardant, smoke suppression, and thermal stability of the material were used to evaluate its performance as a potential construction material. The effect of the addition of glass fiber and the pavement structure of straw and glass fiber were also characterized. The experimental results showed that the mechanical strength and rigidity of SMC composite were increased by the addition of 9% glass fiber to the total mass of the filler. Glass fibers reinforced and reduced the volume of the filler, while increasing the dimensional stability of the composites. The strength of the mixed structural composites was higher than layered structural composites, which is benefits the preparation of the composites. Compared to other straw/cement composites, glass-fiber reinforced SMC composites exhibited better strength, dimensional stability, flame retardant, smoke suppression and thermal stability. These superb properties make these novel composites an ideal candidate for use in the field of interior decoration, particularly in public venues.