Sunflower is an important oilseed crop. Being a deep rooted crop, it can tolerate water or nutrient stress and can be grown in rotation of any crop. Crop simulation models can be an alternative research tool for simulating the growth and yield of sunflower hybrids. The objectives of the present study were to evaluate the performance of the OILCROP-SUN model for three contrasting environments, including arid, semi arid and sub humid conditions. The model also used for determining effect of nitrogen on different sunflower hybrids for these three environments. Field experiments were conducted in three environments to study the impact of nitrogen fertilizer on grain yield. The OILCROP-SUN Model (V 4.0.2) was used to simulate growth, development yield of sunflower. The model was calibrated with the experimental data for the year 2008 and it predicted phenological development of all sunflower hybrids rationally good and RMSE between observed and predicted days to maturity was 0.70, 0.0, and 1.3 days, while in case of achene yield 285, 261, 279 kg ha^-1 and in case of TDM values 2604, 1264, and 2517 kg ha^-1 during model calibration for hybrid Hysun-33, Hysun-38 and Pioneer-64A93, respectively. The OILCROP-SUN model was validated for achene yield using data from experimental trial carried out during 2009. The average error between predicted and observed values was 9.9 % and values for RMSE were ranged from 348 to 1420 kg ha^-1 among all experimental locations of Punjab-Pakistan. Further studies should focus on application of the OILCROP-SUN model for other regions where sunflower is an important crop.