Abstract: Experiments and statistics of the water content of the red clay in Guizhou show that the natural water content and the saturation of the red clay are characterized by a special relationship between the high water content index and the consistency state and with the saturation higher than the theory maximum.By analyzing the special composition and structure of the red clay,it is found that there is a lot of the combined water in the red clay.The "equivalent water content" and "equivalent saturation" are used to amend the water content index and evaluate the red clay.As a result,the unreasonable influence produced by the combined water can be eliminated,and the results are easily compared with the water content index of other soil types.