The relationship between land features and their spectral characteristics is a key for the interpretation of remote sensing images. In this study, the spectral characteristics of a submerged plant Vallisneria spiralis with varied coverage were measured with a ground sensor/radiometer, FieldSpec(tm) Pro JR spectroradiometer in the laboratory and in a constructed wetland “Mengqingyuan", Shanghai. The results showed that the reflectance rate of Vallisneria spiralis increased with its increasing coverage, which exhibited both at the visible band (500～650 nm) and the near infrared band (700～900nm). The water quality influenced the reflectance rate and the primary differences between the laboratory and field experiments mainly occurred at the nearinfrared band (700～900 nm). A regression analysis was carried out between the coverage of Vallisneria spiralis and the reflectance rate at the wavelengths of Quick Bird 4 bands where the coverage responded the strongest, respectively. These results of regression analyses showed a clear linear relationship, and by which the coverage of Vallisneria spiralis could be quantitatively deduced from the reflectance rate measured in situ. The implications of this in terms of the ability of hyperspectral remote sensing to distinguish and monitor the distribution and dynamics of submerged vegetation on a large scale are discussed.