As an important insulating medium for high voltage electrical equipment, epoxy composites have been in the environment of high voltage, high heat and high mechanical stress for a long time, which requires epoxy materials to have high flame retardancy and mechanical strength. In this paper, focusing on the synergistic improvement of flame retardancy and mechanical properties of epoxy composites, epoxy composites were prepared by using magnesium hydroxide inorganic flame retardant fillers and ethylene glycol diglycidyl ether synergistically substitution, and their flame retardant and mechanical properties were studied. The experimental results show that the flame retardant grade of the modified epoxy material is raised to V-0 grade, and when the content of ethylene glycol Diglycidyl ether is 40 wt%, the mechanical properties of the epoxy composite are the best, the tensile strength is 53.72 MPa, the bending strength is 72 MPa, and the impact strength is 10.26 kJ/m2, which is 49.4% and 45% higher than that of the unmodified epoxy material, respectively.