The present invention discloses a thermosetting resin composition including: a bi-functional or multi-functional epoxy resin, a SMA uses as a curing agent, an allyl phenol such as diallyl bisphenol A used as a co-curing agent and a toughening agent a low-bromine or high-bromine BPA epoxy resin or tetrabromobispheno A (TBBPA or TBBA) uses as a flame retardant agent, and an appropriate solvent. After the resin composition of the invention is cured, the resin composition has lower dielectric property and better thermal reliability and tenacity. A copper clad laminate made of an enhanced material such as glass fiber has lower dielectric constant (Dk) and loss tangent (Df), high Tg, high thermal decomposition temperature (Td), better tenacity and PCB manufacturability, and thus very suitable to be used as a copper clad laminate and a prepreg for manufacturing PCBs or applied as a molding resin material for contraction, automobile and air navigation.