Abstract: Leaf area is not only an important external quality trait of flower plants, but also a parameter used in the photosynthesis-driven crop growth model. The aim of this study was to develop a model for predicting the effects of water supply on plant leaf area. For this purpose, experiments of cut lily (Lilium cv ‘Sorbonne’) with different planting dates and different levels of water treatment were conducted in a multi-span greenhouse located at Nanjing from March 2009 to January 2010. Based on the experimental data, the critical water potential for cut lily growth was then determined. The seasonal changes of leaf area of the cut lily plants, and the impacts of substrate water potential on the maximum leaf length (Lmax), the increasing rate of Lmax with leaf rank before the maximum length of matured leaf appeared, the photo-thermal index accumulated from the date when the leaf appears to the date when the leaf reaches its maximal length were quantitatively investigated. Based on these quantitative analyses, a dynamic model was developed for predicting the effects of substrate water potential on leaf area index of cut lily plants. Independent experimental data were used to validate the model. The results showed that the model gave good predictions of leaf area index. The coefficient of determination (r2) between the simulated and the measured values of number of leaf unfolding, individual leaf length and leaf area index were 0.96, 0.82, 0.97, respectively. The relative root mean square error (rRMSE) between the simulated and the measured values were 6.32%,8.78%,7.12% respectively, for number of leaf unfolding, individual leaf length and leaf area index. The model developed in this study can satisfactorily predict the dynamics of the leaf area of cut lily organs, hence, can be used for optimizing water management for cut lily production.