Abstract: Although Van Genuchten model is widely used for fitting soil water characteristic curves (SWCCs), the fitted parameters vary while considering the different forms of parameter and n and whether the largest matric suction point (106 kPa) is involved in the data. Therefore, three forms of parameter ( refers to a) without constraints; b) ; c) , respectively), as well as largest matric suction point were studied in the paper. The relationship between different parameters were discussed and the saturation degrees at matric suction of 106 kPa were calculated using the different parameters under different conditions, which were applied to analyze the relationship of saturation degrees at matric suction of 106 kPa among different conditions. The result shows that in the condition of constrained , discrete degree and interval range of 、 、 decrease when the largest matric suction point is added into the data. Moreover, discrete degree and interval range of decrease and discrete degree and interval range of 、 increase when adding the largest matric suction point under the condition of is not constrained. The results also indicate that the parameter under various conditions of and largest matric suction point shows a linear correlation of parameter without any constraints; but for parameter , the rule does not exist. The saturation degree at the largest matric suction point under various conditions of and largest matric suction point shows a linear correlation of saturation degree at the largest matric suction point without any constraints.

Key words: Van Genuchten model, SWCC, uncertainty, discrete degree, linear relationship