Experimental studies on vertical distribution of cotton leaf nitrogen content per unit leaf dry mass and light response of photosynthesis (Pn-PPFD resonse curve) over canopy depth were conducted at the Yucheng Comprehensive Experimental Station of the Chinese Academy of Sciences during the period from July to August in 2007. Results show that both the mean nitrogen content and the parameters of photosynthetic characteristics including maximum net photosynthetic rate, apparent dark respiration rate, light compensation point and light saturation point decrease with canopy depth, which was divided into three layers ( top, middle and bottom ), while apparent quantum yield is a little different. Based on observations of the vertical distribution of leaf nitrogen content in the canopy on different dates, attenuation coefficient of kn 0.762 changes leaf nitrogen content with a relative cumulative leaf area index in the canopy was modeled as an exponential function.