Despite the great application potential of epoxy resin (EP) modified with polyamic acid (PAA), the large amount of high-boiling-point non-protonic polar solvents used to promote their compatibility cannot be completely eliminated, which affects the fabrication and application of epoxy composites in practical engineering. Herein, PAA was prepared by solvent-free ball milling method, and then the primary amine hyperbranched polysiloxane (HSiNH2) was prepared by “one-pot” method as the “bridging structure” to improve the compatibility between PAA and EP. Compared to neat EP, the flexural, impact and tensile shear strength of the epoxy composite are increased by 22.2%, 30.0% and 23.2%, while the average friction coefficient and volume wear rate are reduced by 26.5% and 20.6% under the contents of PAA and HSiNH2 are 1.50 wt% and 2.0 wt%, respectively. Moreover, the material exhibits excellent thermal properties. By comprehensively analyzing the structure and properties of the epoxy composite, it is mainly ascribed to the fact that HSiNH2 with a large number of reactive groups acted as a “bridging structure” to enhance the compatibility of PAA and EP, which results in the epoxy composite having excellent mechanical, tribological and thermal properties. This research also lays the theoretical foundation for the development of high-performance epoxy composites in aerospace.