Ceramifiable ethylene-vinyl acetate (EVA) copolymer composites were prepared through incorporating silicate glass frits (SGF) and ammonium polyphosphate (APP) into the EVA. The ceramic residues were obtained by firing all samples at different temperatures. The effect of APP on the self-supporting property and shape stability of the composites were studied, and the effect of APP on the flexural strength and water absorption of the ceramic residues were investigated. The results show that the addition of APP improved the self-supporting property and the flexural strength of the composites due to the increased crystal phase. The shape stability and the porous structure of the residues increased due to water and NH3 released from the thermal decomposition of APP. XRD and SEM analysis demonstrated that APP promotes the precipitation of sodium phosphate and cristobalite. Furthermore, the growth process of the crystal was investigated by crystallization kinetic.