Abstract: Epoxy resin was toughened using polyether sulfone(PES) forming TDE85/PES composite systems. The effect of PES on the thermomechanical properties of the composite was studied using SEM,DMA,DSC, and FTIR. It showed that the mechanical strength and glass transition temperature (Tg) of the epoxy resin was improved obviously by adding PES. When the mass content of PES was 8.00 %, the tensile strength, elongation at break, and impact strength of TDE85/PES composites were increased by 20.60 %, 29.29 %, and 44.20 %, respectively. Micromorphological study showed that the TDE85/PES system possessed a two phase structure. The deformed PES particles were dispersed in the epoxy resin matrix. The toughening effect of PES was caused by the formation of an SIPN in TDE85/PES system, and the deformed PES particles in the epoxy matrix under high stresses.