| The bismaleimide resin is a novel matrix material for the high-performance carbon fiber composites, which possesses wide application in the aeronautic, astronautic and the other fields. Nowadays, the evaluations of the modification technique, the preparation technology, the material performance, etc., of the relevant materials mainly depend on the experimental methods, and the numerical models and the relevant algorithms still lack. In this work, the molecular models of 4, 4'–diphenylmethane bismaleimide (BDM) and the diallyl bisphenol A (DABPA, curing agent) are constructed, and the cross-linking reaction which is consistent with the experimental process is also achieved. The mechanical property of the BDM/DABPA resin and the corresponding change induced by filling with the carbon nanotubes are examined, respectively. The results indicate that the mechanical property of the bismaleimide resin increases with the increase in the degree of cross-linking, which could also be further enhanced by filling with the carbon nanotubes. The present work establishes a numerical method for the composites design based on the bismaleimide resin, and the findings provide a valuable reference for the modification of the relevant materials from the microscale level.