I want to supply under 1.1V to xilinx virtex5 Vccint how to make the volatage?
It's usually a good idea to check the reference designs.

A typically solution would be to use a step-down converter as shown below


The output voltage can be set by resistor R195. With this specific regulator the lowest possible voltage is around 0.65V.

For details you can check the datasheet of the PTH08T220W