The productivity is a critical component of the terrestrial carbon cycle. Remote sensing driven light use efficiency models have been widely utilized to calculate the productivity of terrestrial ecosystems. They calculate the productivity as a linear product of maximum light use efficiency ε_max, scaling factors of environmental stress, and absorbed photosynthetically active radiation (APAR). The outputs of these models are very sensitive to t maximum light use efficiency (ε_max), which represents the utilization rate of photosynthetically active radiation under ideal conditions without restrictions. However, it is difficult to determine this parameter properly since it is affected by numerous factors, including canopy nitrogen content, atmospheric concentration of CO₂, plant types and species, and exhibit significant spatial and temporal variations. In currently used light use efficiency models, this parameter only changes with plant types. Such simplified parameterization might induce large uncertainties in calculated productivity of terrestrial ecosystems at regional and global scales. In this study, MODIS reflectance data, county\level yield census data, locally observed meteorological data, and the vegetation photosynthesis model (VPM) were employed to derive annual mean county\level cropland ε_max in Jiangsu province for the period from 2001 to 2010. The county\level yield census data was converted into total net primary productivity of each county for estimating the ε_max parameter in the VPM model. Then, the spatial and temporal variations of ε_max and possible driving factors were analyzed were analyzed. The results show that the county\level means of cropland ε_max in 61 counties of Jiangsu province varied between 0.757-3.435 g C/MJ during the period from 2001 to 2010, with an overall gradient decreasing from the north to the south. It is higher in the central areas than in the surrounding areas. Annual mean cropland ε_max increased during the period from 2001 to 2010 in all 61 counties, but showed obvious interannual fluctuations during the period from 2001 to 2006. It was relatively lower in years 2002, 2004 and 2006 and steadily increased in all counties since 2007. The interannual fluctuations of ε_max were normally higher in the north than in the south. The annual means of ε_max were positively related to the amount of fertilizer used in per unit area of cultivated cropland in most counties, particularly in the northern areas of Jiangsu Province. The increasing rates of ε_max were positively correlated with the increasing rates of fertilizer utilization per unit area. The interannual fluctuations of ε_max were also related to the yield fraction of C₄ crops (corn). This study proves that it is of importance to develop a parameterization scheme accounting for the temporal and spatial variations of ε_max for improving the calculation of productivity in croplands using light use efficiency models and remote sensing data. It should be kept in mind that some factors might induce uncertainties estimated ε_max, such as the uncertainties in yield census data, the parameters used to converts yield into net primary productivity, methodologies used to calculate APAR and scaling factors of environmental stress. The underlying mechanisms for driving significant spatial and temporal variations of ε_max need further thorough investigation. Nevertheless, the findings in this study can provide a value reference for optimizing the calculation of carbon fluxes between the atmosphere and terrestrial ecosystems.