Abstract: This paper firstly provides a new point that the existence of magnetic monopoles will break the electro-magnetic duality symmetry of electrodynamics spontaneously and points out the existence of relevant goldston bosons; then analyzes the difficulties encounting the electrodynamics action description and expressed the viewpoint that electrodynamics containging no magnetic monopoles is more symmetric than that containing them; finaly makes a simple introduction to the concept of two kinds of magnetic monopoles.

Key words: magnetic monopoles, electro-magnetic duality symmetry, spontaneous symmetry breaking