PCIe versions are all supposed to be backwards-compatible except sometimes for PCIe 2.1 cards and PCIe 1 variants such as 1.0a and 1.1. PCIe 2.0/2.1 will work in PCIe 3.0 slots and those slots will work as PCIe 2.0 if the CPU only supports up to PCIe 2.0.
PCIe 3.0 motherboards all support PCIe 2.0 and other versions. For example, a lot of Z68 boards supported PCIe 3.0 before there were any PCIe 3.0 LGA 1155 CPUs and the Sandy Bridge CPUs all work on them in PCIe 2.0.
Basically, don't worry, your system will work.
A lots of "thanks" for the reply;
Then my graphic card will work with full bandwidth on ASRock H77 Pro4/MVP with Intel core i3 3220 on PCIE 3.0X16 slote...........