Heidi Klum was back in beach mode on St. Barts, showing off her incredible physique in a bikini with her hubby Tom Kaulitz at her side.

The lovebirds were enjoying some more fun in the sun Tuesday on the beautiful Caribbean island, where they've been vacationing for about a week.

Check out new photos, obtained by TMZ ... Heidi and Tom are glued to each other as they frolic on the sand and in the water. They appear to be madly in love with Heidi at one point cracking a big ol' smile.

And, why wouldn't she? Life couldn't be any better for the model. She's livin' it up with her man seemingly without a care in the world.

You may recall last week ... the couple was snapped kissing passionately on the same beach and splashing around together in the sea.

Cheers you two!