Models describing the light response of photosynthetic electron transport rate (ETR) are routinely to determine how light absorption influences energy (ATP),reducing power (NADPH) and yields of primary productivity;however,no single model is currently able to provide insight into the fundamental processes that implicitly govern the variability of light absorption.Here we present development and application of a new mechanistic model of ETR for photosystem Ⅱ based on the light harvesting (absorption and transfer to the corereaction centers) characteristics of photosynthetic pigment molecules.Within this model a series of equations are used to describe novel biophysicai and biochemical characteristics of photosynthetic pigment molecules and in turn light harvesting specifically,the eigen-absorption cross-section and the minimum average lifetime of photosynthetic pigment molecules in the excited state,which describe the capability of light absorption of photosynthetic pigment molecules and retention time of exciton in the excited state but are difficult to measure directly.