This specification discloses an integrally formed safety helmet. A pre-cast hard outer shell is directly filled with Styrofoam particles followed by heating and pressing to form a soft inner shell. The two shells are integrally formed and tightly connected with no space in between. The production procedure includes the steps of: putting a pre-cast hard outer shell in an upper mold; combining the upper mold and a lower mold; heating the molds to soften a compound material outer shell; pressing to squeeze out extra resin in the compound material outer shell; cooling down the molds and injecting Styrofoam particles into the cavity in the molds, foaming, pressing, and lowering the temperature; and removing the molds. The soft inner shell is then integrally formed inside the hard outer shell.