The main point of the hydrodynamic model of electromagnetic field [13,14] is that; the motion of the electromagnetic field can be divided into two parts, the orbital motion and the intrinsic motion. In this paper we to define intrinsic angular momentum deduced from the intrinsic motion and a related i (imaginary number) operator. Besides, the conservation property of the intrinsic angular momentum, the relations between the spin angular momentum and the intrinsic angular momentum of an electroma-gnetic field are described.