Today I was gona to replace the Rear brake disc 320mm on mine S 320 2007.
But cant fit in bracket.

dose any one have solution for this? Can I buy rear brake caliper bracket from S500/S550, would it fit?

 

The caliper won’t fit either ... you can’t fit thicker rotors without lots of effort. The original parts are fine, perfectly engineered by Mercedes.

 

The rear disc is a solid style disc, not a ventilated one. You most likely have a front disc there when you need the proper rear one.

 

When I still had my W220 S500 I got a learning experience. I ordered brake parts from either rockauto or amazon, for a typical 2002 S500. Didn't realize the parts were wrong but I had placed one of the pads facing away from the disc. Crazy, I know. Got a friend of mine who is a Boeing engineer (a brilliant guy) to come over and take it all apart. He said the parts were wrong, in addition to being installed wrong. So I called a Benz dealership with the car's VIN, their computers know the exact parts and part numbers for the right brakes for the car. they will give you this information for free. Found out the car had AMG brakes, which, when received the right parts, were quite different from the others. Now I won't do a brake job on a Mercedes without first getting the part numbers for the discs, pads, etc., and most often of course, those exact parts can be bought online for less money than a dealership wants to charge. But knowing the exact part numbers that came with the car, guarantee you that you're putting on the right stuff. In some instances, if you don't have AMG Brakes or whatever, you might be able to upgrade with a different manufacturer's parts. If your came factory with AMG brakes, however, I would stay with those, it would be hard to improve upon! And I do agree, that I believe that vented disc is for the front, and the solid, somewhat thinner disc is for the rear. Then you'll have no problem.
I learned about Mercedes brakes one day years ago when I took my 1990 300CE to a shop, my "get some new brakes" light was illuminating in the cluster. They wanted $400 to install new front brake pads. Period. I said, I'll come back on Payday. Instead I bought new pads and found a YouTube video that showed how easy it was to simply replace pads.
Took 30 minutes and I saved $350. Benz brakes are some of the easiest in the world, so long as you don't put a pad on backwards! LOL

 

That looks like the right style of rotor for the rear axle, but I bet it's for an AMG W221. As mentioned before, non-AMG rear rotors are solid, not drilled/vented.

 

that depends on the spec.... mine has vented both ends
there are three brake set ups (not the correct names) but
-
basic
big, both front rear vented
AMG