Abstract: In order to explore comprehensive impact of drought occurrence and development process on photosynthetic characteristics and water use efficiency of cotton at the leaf scale under mulch drip irrigation in the key period of cotton, five drought simulation experiments with different water gradients were carried out to analyze effects of drought occurrence and development with different intensities on cotton photosynthetic characteristics and water use efficiency．Results showed that photosynthetic characteristic parameters（net photosynthetic rate, stomatal conductance, transpiration rate, intercellular CO₂ concentration）of leaves increased first and then decreased with advance of growth process．After 9 days of gradient water control, each treatment entered a different drought development process, and photosynthetic characteristic parameters of each treatment decreased in turn．Drought stress did not change trend of water use efficiency of cotton leaves．Water use efficiency of cotton leaves under five different gradient water treatments showed an upward trend during flowering and boll stage, but its change was not regular．Research results could provide theoretical basis for accurate evaluation of cotton drought degree and dynamic monitoring of drought occurrence and development．