Abstract: In order to study micro-structure and properties of composite, polyether sulfone/bismaleimide-epoxy composite was prepared by in-situ polymerization. The results of FTIR and SEM show that PES do not react chemical reaction with BMI-EP, PES is existence of two-phase structure in composite and has very strong interaction with BMI-EP matrix. PES presente as disperse phase in matrix, the interface of PES and matrix is fuzzy. The failure crack is not smooth and the direction is changed, it is typical ductile fracture when PES is added into the polymer matrix. The energy spectrum analysis show that PES is mutual penetration phenomenon with matrix and PES is uniformly dispersed in the matrix. The results of mechanical properties indicated that the toughening effect of PES resin are extremely obvious, when the content of PES is 4 wt%, the bending strength and the impact strength of PES/BMI-EP are 144.9 MPa and 19.7 kJ/m², 41.2% and 90% higher than that of BMI-EP matrix, respectively. The thermogravimetric results prove that appropriate amount of PES can improve the heat resistance of PES/BMI-EP composite, and the excessive amount of PES resin is not conducive to the decomposition temperature of the material.