can I put 2 Radeon 6850 in my computer I have a 530w PSU and my motherboard is a Gigabyte GA-970A-UD3 .
your board does support crossfire at 1= pciex 16 2= pciex 4 but your psu will want upgrading but to be honest instead of buying 2 x 6850 buy 1 and get a better psu becaus you wont see much benifits with 2 x 6850s in this board.
If that's a good 530W unit, it can handle two HD6850s just fine. The minimum I'd recommend for two 6850s is 500W. However, if it's a cheap unit like Rosewill or Raidmax, you will need a new PSU first.