The Leaf Area Index（LAI） is essential in the remote sensing of vegetation

and is widely used in quantitative remote sensing products. LAI products should be validated to enable their effective applications in various fields. In this study

the indicators and methods of LAI product validation were investigated

and a process for LAI product validation was established. The grassland in Xilinhot

Inner Mongolia of China was selected as the study area. Landsat TM data and ground measurements were used to build the Normalized Difference Vegetation Index（ NDVI）-LAI model. Then

the "true"LAI reference for validation was established. The MODIS LAI product was also validated in this study according to the reference LAI and the proposed model. In addition

the sources of error in the MODIS LAI product were analyzed. Results showed that the MODIS LAI product（ i. e.

MOD15A2） in the study area was overestimated by approximately 25%. Among the factors that affected the error

the difference in LAI remote sensing models was the most dominant

leading to an overestimation of 44. 2% in the MODIS LAI model. Meanwhile

image quantitative difference exerted a significant influence

causing an underestimation of approximately 16. 2%. In addition to these two factors

the scale effect produced an underestimation of 3. 1%

including an underestimation of 2. 4% from the scale effect of the NDVI-LAI model

and an underestimation of 0. 7% from the scale effect of NDVI.