Bismaleimide (BMI)/allyl-functional phthalonitriles-containing benzoxazine (BA-ph) prepolymers were prepared via solution prepolymerization. The corresponding curing behaviors and processability were investigated by differential scanning calorimetry and dynamic rheological analysis. The results indicated that BMI/DABA-Ph prepolymers exhibited better processability due to the introduction of allyl moieties and benzoxazine rings. The resulting copolymers showed high thermo-oxidative stabilities which was attribute to the introduction of phthalonitrile. In addition, the possible curing reactions were studied by Fourier transform infrared spectroscopy. A series of reactions may be involved, which contained the ring-opening polymerization of benzoxazine rings, the polymerization of phthalonitrile, self-polymerization of BMI, and the ene reaction between allyl group and imide group. Moreover, BMI/DABA-Ph prepolymers were employed to prepare BMI/DABA-Ph/glass fabric (GF) composite laminates and their mechanical and thermal properties were investigated. The BMI/DABA-Ph/GF composite laminates showed relatively better mechanical properties and satisfactory thermal properties. This study provided a method for diversifying the preparation of BMI/DABA-Ph prepolymers to obtain advanced GF composite laminates with various properties, which have potential applications in industrial manufacture, especially in the areas which require excellent mechanical properties and high temperature resistance.