O,O'-diallylbisphenol A ( BA), allyl epoxy resins and epoxy acrylate resins are adopted to copolymerize with 4,4'-bismaleimidodiphenyl methane ( BDM) resins and modify mechanical properties and processing charicteristics. The new modified BMI resin systems have more than two times improved impact strength without a great decrease in excellent dielectric properties or thermal and hot-wet resistance of neat BDM resin. Composites based on modified BMI resins and reinforced by glass fibre and quartz fibre possess excellent mechanical properties. The fracture surfaces of the composites are examined by scanning electron microscopy ( SEM). It is indicted that modified BMI resin matrix composites put up typical toughness rupture and the adhesion efficiency in interface of composites is fine. When the test frequency scope is from 1GHz to 20GHz, the dielectric constant and dielectric loss of composites almost hold the line. After 100h in boil water, mechanical and dielectric properties of composites are higher than 85% retention of their original values.