A high thermal-conductive, halogen-free and flame-retardant resin composition used as a dielectric layer of a printed circuit board comprises 5% to 70% of phosphorus-containing epoxy resin, at most 50% of multifunctional or bifunctional epoxy resin, 1% to 20% of curing agent, 0.01% to 10% of accelerant, at most 20% of inorganic powder, 5% to 85% of high thermal conductivity powder and 0.01% to 10% of processing aids, which resin composition has excellent thermal conductivity, heat resistance and flame retardancy as well as being environmentally friendly for free of halogen flame retardant and no toxic or corrosive gases when burning; the resin composition is used to form as a high thermal-conductive prepreg by impregnation or form as a high thermal-conductive coating by coating and then further used as a dielectric layer on a printed circuit board for demonstrating if electronic components formed thereon the printed circuit board has high thermal-conductivity and efficient heat dissipation capable of improving long service life and enhanced stability of electronic components.