In order to estimate vegetation index precisely

the soil lines of different soil types must be identified.However

it is difficult to obtain the soil line parameters

because there are many influencing factors.With the laboratory soil hyperspectral reflectance studied

the main factors influencing the soil line were determined.The laboratory soil hyperspectral reflectance was used to calculate soil line parameters

which were introduced to compute the vegetation indices related to soil line.The correlation between the indices and soybean chlorophyll a or leaf area index（LAI） was compared with that between normalized difference vegetation index（NDVI） and chlorophyll a or LAI

then the feasibility of the soil line computing method was analyzed.The results were as follows: the main factors affecting soil line parameters were not the band width but the soil class

the latitude

organic matter

mineral composition

and straw residues.Soil classes

with different physical and chemical properties

show significant differences in spectral characteristics

especially the reflectance shape at red and infrared bands.The slope of soil line with low soil albedo was not always smaller than that with higher soil albedo.What’s more

latitude also influenced the soil line parameters because of the regular distribution of soil parent material and other soil properties.The effect of organic matter on soil reflectance in visible and infrared bands（620—810nm） is much stronger than other spectral regions

the reflectance curve at visible and infrared domain is concave

so the slope of soil line increases with organic matter content.What’s more the effect of organic matter on soil line parameters may be stronger than soil class.Based on soil line

the soil vegetation indices partly eliminate the soil background noises

and the correlation between the indices and soybean chlorophyll a or LAI is more significant than that between NDVI and chlorophyll a or LAI

which indicates that the soil line parameter deriving method is feasible and appropriate for the vegetation indices based on soil line.In order to enhance the monitoring precision of vegetation indices

the soil line parameters should be calculated based on the spatial difference of the main factors influencing the parameters.However

the results of the study is based on ground crop spectral reflectance data and obtained in the laboratory

as a result

the influence of atmosphere is not completely considered.Therefore

when the result is used in remote sensing image data

the influence of atmosphere on soil and crop reflectance must be analyzed.