Understanding unidentified Fermi sources is significant in gamma-ray astronomy. A large portion of the unidentified Fermi sources are blazars that are radio-loud active galactic nuclei with peak emission at millimeter wavelengths. The millimeter regime has been proved to be the one of the most efficient means to identify both blazars and unidentified Fermi sources. The South Pole Telescope with arcminute resolution at millimeter wavelengths has completed a survey covering a large fraction of southern extragalactic sky. Preliminary analysis shows that SPT point source catalog provide candidates associated with unidentified Fermi sources to greater than forty percent. This study will perform profound millimeter/gamma-ray connection and uncover the mystery of nature of the unidentified Fermi sources.Ope
