By Mössbauer spectroscopy, NAA and optical spectroscopy, the coloring and the firing technology of ancient Ru celadon were studied. Also, the relationship between Ru Kuan celadon from Qingliang Temple and Ru celadon from Zhanggongxiang was studied by PIXE. The glaze color of Ru celadon depends on the ratio of the structural iron ions, i.e. the Fe 2+ /Fe 3+ ratio. Further, it depends on the firing conditions. As the Fe 2+ /Fe 3+ ratio gradually increases, the glaze color of Ru celadon will gradually change from pea green to sky green. All the Ru celadons were fired in a reducing atmosphere. The sky green Ru celadon was fired in the most reducing atmosphere and at the highest temperature, the powder green in a more reducing atmosphere and at a lower temperature and the pea green in a lightly reducing atmosphere and at the lowest temperature. The PIXE experimental results showed that Ru Kuan celadon from Qingliang Temple and Ru celadon from Zhanggongxiang were incompletely identical in the recipe of glaze and they could be differentiated by the cluster analysis of the major element concentration of glaze.