We report a surface segregation approach to synthesize high quality graphenes on Ni under ambient pressure. Graphenes were segregated from Ni surfaces by carbon dissolving at high temperature and cooling down with various cooling rates. Different segregation behaviors were identified, allowing us to control the thickness and defects of graphene films. Electron microscopy and Raman spectroscopy studies indicated that these graphenes have high quality crystalline structure and controllable thickness. Graphenes were transferred to insulating substrates by wet etching and were found to maintain their high quality.