Light use efficiency is defined as the ratio of gross primary production or net primary production against the absorbed light energy by vegetation canopy. The quantification modeling of gross primary production or net primary production is based on the quantification modeling of light use efficiency to some extent. Therefore, quantifying light use efficiency at various spatial and temporal resolutions is significant for global carbon cycle because quantifying primary production at various spatial and temporal resolutions is one important component of quantifying global carbon cycle. Alpine meadow is one typical vegetation type on the Qinghai-Tibet Plateau. It is a typical ecosystem in both the Central Asia and the world. Meanwhile, alpine meadow plays a very important role in regiononal carbon budget in China. Hence, quantifying light use efficiency of alpine meadow ecosystem is very important for quantifying region carbon budget on Qinghai-Tibet Plateau. We modeled the light use efficiency of three alpine meadow ecosystems along an altitudinal gradient (4300-4700 m) on the Northern Tibetan Plateau by using the vegetation photosynthesis model in this study. The light use efficiency is determined by two attenuation scalars, land surface water index and air temperature in the vegetation photosynthesis model. Land surface water index can reflect the effects of land surface water content and vegetation phenology on the light use efficiency in the vegetation photosynthesis model. The mean values of the light use efficiency on altitudes of 4300 m, 4500 m and 4700 m were 0.38 g C/MJ, 0.47 g C/MJand 0.35 g C/MJ, respectively. Analysis of variance showed that the light use efficiency on altitude 4500 m was significantly higher than those on altitudes of 4300 m and 4700 m. Besides, the light use efficiency difference between altitude of 4300 m and 4700 m was not significant. Simple linear correlation analysis and multiple stepwise linear regression analysis between light use efficiency and soil temperature, soil water content, air temperature, relative humidity and land surface water index showed that the seasonal change of the light use efficiency was determined by air temperature, relative humidity and land surface water index on all studied altitudes. Air temperature, relative humidity and land surface water index together explained at least 99% of seasonal change of the light use efficiency. The standard regression coefficient of air temperature was the largest, followed by relative humidity and then by land surface water index. Therefore, the contribution ranking of each factor to the light use efficiency regression equation was air temperature > relative humidity > land surface water index on all altitudes. This indicated that the influence of temperature on seasonal change of light use efficiency was larger than water. Multiple stepwise linear regression analysis showed that growing season average soil water content was the dominant factor controlling the spatial variations of growing season average light use efficiency along the altitudinal gradient. Single linear regression analysis showed that land surface water index significantly explained seasonal changes of soil water content and relative humidity on all altitudes. Land surface water index on altitude of 4500 m and 4700 m also significantly explained seasonal changes of vapor pressure deficit. Additionally, seasonal changes of vapor pressure deficit on altitude of 4300 m was explained by land surface water index to some extent. These results indicated that land surface water index could quantify the seasonal change of environmental water content of land surface in the alpine meadow ecosystem. Thus, it is feasible to use land surface water index to infer the water attenuation scalar for the alpine meadow ecosystem on the Northern Tibetan Plateau.