In this paper, commercial Ce-W cathode was selected as research object. The cathode working environment was simulated by heating in an ultra-high vacuum (UHV) chamber. Scanning electron microscopy (SEM), Nano-scanning Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to study the surface morphology and chemical states from 900 degrees C to 1200 degrees C. The results showed that W6+ disappeared and the surface of the cathode was composed entirely of W-0 in heating process. The content of Ce4+ gradually decreased by heating and cerium oxide had a tendency to reduce. The adsorbed oxygen disappeared and the lattice oxygen was present in CeO2 and Ce2O3. Moreover, when raising heating temperature, the rare earth oxide diffused from the aggregation areas to the tungsten matrix surface to form an active layer. The surface cerium oxide was highest at 1100 degrees C. Then the thickness of active layer was about 6 nm. At 1200 degrees C, the evaporation rate of cerium oxide on the surface was greater than the rate of migration from the body to the surface. And the loss of the surface active layer was severe at 1200 degrees C.