A series of experiment were performed to test the tribological properties of Si3N4 ceramic pair lubricated by emulsions of alkane. The experiment results showed that all alkane are very efficient lubricator for Si3N4 ceramic pair. The straight chain alkanes can perform better than branched paraffin or polycyclic saturated hydrocarbon. When added the liquid paraffin with chlorinated paraffin or Oleic acid, the lubrication property become poor. But added with silicone oil emulsion，the lubrication improve further. Base on the molecular structure of reagents, the causative mechanisms is investigated.