Abstract: The 4,4′-diaminodiphenylmethane bismaleimide (BDM)/4,4′-o-diallylbisphenol A (DABPA) resin system was modified by synthesized thermoplastic polyimide (PI) via pre-in situ polymerization, used to prepare modified bismaleimide resin with high heat resistance (BDPI). The micromorphology and heat resistance of BDPI resin were investigated. The T800H carbon fiber/BDPI prepreg was fabricated through pre-in situ self-strengthening technology. The surface morphology of T800H/BDPI prepreg was studied by SEM. The mechanical properties and fracture morphology of T800H/BDPI composites at room temperature and high temperature were evaluated. The results show that the BDPI resin is suitable for prepreg processing technology, and the BDM microparticles with 30–70 μm size are well covered on the surface of T800H/BDPI prepreg. The glass transition temperature (T_g) and 5% mass loss temperature (T_d5) of the cured BDPI resin reach 367℃ and 452℃, respectively. The 0° tensile strength, 0° tensile modulus and interlaminar shear strength of T800H/BDPI unidirectional composites are 2 440 MPa, 148 GPa and 107 MPa, respectively, the retention of which are approximately 66.4%, 87.2% and 44.1% at 280℃, respectively.