During an appearance on Oprah, Hawn revealed that she has no desire to test her commitment to Russell by tying the knot.
"I don't want to ruin it," she said.
The Oscar winner added: "I think marriage can incarcerate if you do it for the wrong reasons... I'm a caged bird but I need the door open."
The couple, who began dating in 1983, are parents to 25-year-old son Wyatt.
Hawn also asserted that she is very happy that her daughter Kate Hudson is expecting a child with Muse frontman Matthew Bellamy.
She beamed: "We're so excited."