A halogen-free and phosphorus-free resin formulation, prepared by the following method, is provided. The method includes mixing a carboxy anhydride derivative, diisocyanate, a styrene maleic anhydride (SMA) copolymer derivative and a solvent to form a mixture, and heating the mixture to form a resin formulation. The disclosure also provides a halogen-free and phosphorus-free composite material with a low dielectric constant and flame resistance prepared from the resin formulation.