Chromium has various valence states and in the process of preparing chromium oxides with low valence state of chromium, chromium compounds with different valence state of chromium can usually be produced as intermediates. Due to the difference in property of these intermediates, they always have remarkable influences on the morphological characteristics of the final product. The composition of the intermediate was very complicated in the process of synthesizing chromium oxide with low valence state of chromium by reducing potassium chromate with hydrogen. To explore the reaction mechanism and further optimize the technical process, the composition of the intermediate obtained from the reduction of K2CrO4 with hydrogen was investigated through the combination of XPS, FTIR and XRD. The XPS results revealed that the intermediate of reducing potassium chromate with hydrogen is trivalent chromium compound; the results of FTIR and XRD indicated that the intermediate mainly consists of Cr(OH)3 x nH2O, HCrO2 and a little amount of KOH or KCrO2. On the basis of the above analysis of the intermediate, the possible reactions that occurred in the reduction process were suggested.