Abstract:Remote sensing technology has provided a rapid, nondestructive method for establishing relationships between photochemical reflectance index (PRI) and photosynthetic light use efficiency (LUE) that is an important parameter for estimating net primary productivity (NPP). Therefore，PRI opens a new era of estimating NPP that can overcome the shortcomings of the empirical model in obtaining LUE through information on temperature and water content. Many studies have demonstrated that a reliable relationship between PRI and LUE could be obtained at leaf, canopy and site scales. However, numerous confounding factors such as water content, leaf nitrogen concentration, and leaf area index and sun zenith angle have emerged as scale changed, leading to disjunctive relationship between PRI and LUE. Thus， the functions of different factors on the relationship between PRI and LUE are important in understanding the mechanism for LUE estimation. This paper analyzes the confounding factors in establishing relationships between PRI and LUE and outlines possible improvements. Further research is needed on the different mechanism of reflectance at 526 nm and 545 nm relating to reflectance at 531 nm， the saturation problem of PRI with increase of LUE and the time and scale effects in estimating LUE with PRI.