You have this girl you love, but your parents don't approve?

[edit] Steps

Talk to your parents. Explain to them that you love the woman and you wish that they could understand that and hope that they will.
Tell them about her. Tell them about her: career/job, place she lives, what kind of girl she is, is she kind? Tell them what she thinks of the world today.
Ask them if they love you. If they say yes, then ask them "Then why won't you two let me marry someone?" Ask them if they love each other, and if they say yes, ask them "Then why can't I love someone?"
Let the parents meet the girl. Tell her all about your parents and tell her they haven't consented yet. Ask her to show what she is really like and her personality.

[edit] Tips

Show the girl and the parents around on a cruise, journey or just a picnic in the park. Allow them to get to know one another.
Show the parents a picture of her before they meet her so they will know what she looks like.
Tell them that you love her and if they cannot accept that, they cannot accept you.