We are not given the kind physical description of Haemon in Antigone that we might expect in a modern novel or play. This allows us to use our imaginations to paint our own picture of what he looks like.
However, the context of the play offers some general clues about him. The play repeats over and over that Haemon is young, and his father, Creon, refers to him at one point as an adolescent. This would put his age in his late teens. His betrothal to Antigone also supports the idea of his late teens, as that was the time an aristocratic Greek youth would expect to be married.
We can infer that Haemon, a youthful and well-fed royal son, is vigorous and handsome. We can also infer that he is physically strong. He lunges at his father with a sword in Antigone's tomb, and he then turns the sword on himself and stabs himself through over his fiancée's death. As Greek plays tend to note when an important figure has a handicap, we can assume that Haemon, as also supported by his ability to wield a sword, is able bodied.
Other than this, we get no information about his appearance, such as hair or eye color, height or weight. What is more important to Sophocles is Haemon's character and spirit in opposing his father.