To provide a method for forming a fan blade used in a cooling tower fan, at the cost inexpensive such that the conventional method could not achieve.

In a mold having inner wall corresponding to the outer shape of a fan blade 10, an elongated support 12 extending longitudinally along with the blade and having protrusions 14 are positioned. A rotative forming method is used in which the thermo plastic material is introduced into the mold, and then to heat and to rotate the mold to embed partially the supporting member into the plastic material, such that the amount of the plastic material is selected as if the eventually obtained blade is to have a hollow cavity.