Through analyzing and extracting the newest research results on nitrogen and water management of cotton, a dynamic knowledge model for decision-making on total nitrogen and water supply levels and their distribution among main growth stages of cotton under different environments and yield targets was developed, with the principles of nitrogen balance and water demand and by integrating the factors of climate, soil, yield and variety. Case studies on the knowledge model with the experiment data sets of different eco-sites, varieties and soil characters indicated a good model performance in decision-making and applicability.