To improve the performance of traditional polybenzoxazines, copolymerized 3-phenyl-3,4-dihydro-2H-1,3-benzoxazine (Pa) and bisphenol-A benzoxazine (Ba) with three kinds of cyclotriphosphazene (CP)-based benzoxazine monomers, respectively. The ring-opening copolymerization behaviors of the benzoxazines mixtures are investigated by differential scanning calorimetry (DSC), the results imply that the CP-based benzoxazines could decrease the polymerization temperature of common benzoxazines. Due to the different structures of the CP-based benzoxazines that possess different numbers of organic benzoxazine moieties tether onto the inorganic CP ring, they produce the different dimensional crosslinking structures of the CP-based benzoxazines under ring-opening polymerization, the TGA and DMA results display the CP-based benzoxazines exhibit different degrees of improvement on the thermal stability and mechanic properties to the co-polybenzoxazines.