The present invention discloses a thermosetting resin composition comprising: a bifunctional or multifunctional epoxy resin, a styrene-maleic anhydride (SMA) copolymer with a styrene / maleic anhydride molar ratio of 5-12:1 as a curing agent, a BPA epoxy resin with a low or high bromine content or tetrabromobisphenol A as a flame retardant agent, an accelerator and a solvent. The cured resin composition of the invention has a very low dielectric property, improved thermal reliability and better toughness. A copper clad laminate made of the resin composition and a reinforced material such as glass fiber cloth has a very low dielectric constant and dissipation factor, high Td, better toughness and PCB manufacturability, and thus very suitable to be used as a copper clad laminate and a prepreg for manufacturing PCBs and also applied to the common use of epoxy resins, such as molding resins, and composite materials for construction, automobiles and aviation.