DECISION SUPPORT SYSTEM FOR AGROTECHNOLOGY TRANSFER (DSSAT) MODEL IS ABLE TO SIMULATE CROP GROWTH, DEVELOPMENT, AND YIELD THAT ARE GROWN ON A UNIFORM SURFACE UNDER SIMULATED MANAGEMENT CONDITIONS, INCLUDING CHANGES IN SOIL WATER CONTENT, SOIL CARBON CONTENT, SOIL NITROGEN CONTENT AND NITROGEN LEACHING. THIS STUDY WAS AIMED TO INVESTIGATE THE EFFECTS OF NITROGEN ON YIELD AND YIELD COMPONENTS OF MAIZE VARIETY SC704 USING THE MODEL, AND TO CALIBRATE CERES-MAIZE MODEL UNDER 4 LEVELS OF NITROGEN FERTILIZER: N1: 25% LESS THAN THE RECOMMENDED LEVEL, N2: RECOMMENDED LEVEL (200 KG/HA), N3: 50% LESS THAN RECOMMENDED LEVEL (260 KG/HA), AND N4: 50% MORE THAN THE RECOMMENDED LEVEL (310 KG/HA). IN THIS CASE, AN EXPERIMENT WAS PLANNED BASED ON RANDOMIZED COMPLETE BLOCK DESIGN WITH THREE REPLICATIONS, AND CONDUCTED DURING 2013 AT THE RESEARCH FIELD OF AGRICULTURE FACULTY OF ISLAMIC AZAD UNIVERSITY – KARAJ BRANCH. THE MEASURED AND SIMULATED VALUES OF EAR YIELD, BIOMASS, LEAF AREA INDEX (LAI) AND STEM DRY MATTER CONTENT WERE COMPARED. THE RESULTS OF THE BIOMASS SIMULATION SHOWED THAT ROOT MEAN SQUARE ERROR (RMSE) OF THE FOUR FERTILIZER LEVELS HAVE RANGED RESPECTIVELY 2496.48, 2159.24, 2302.43, AND 3289.19 KG/HA. FOR THE EAR YIELD, THE HIGHEST COEFFICIENT OF DETERMINATION (R2=0.98) WAS OBTAINED BY N4. IN FACT, THIS TREATMENT PROVIDED HIGHEST ACCURACY FOR PREDICTING THE YIELD OF MAIZE BY THE MODEL. FOR LEAF AREA INDEX, THE WILLMOTT AGREEMENT INDEX (D) VARIED BETWEEN 0.77-0.94. THIS INDICATES THAT THE MODEL HAS SUCCESSFULLY PREDICTED THE VARIATION OF LEAF AREA INDEX. THEREFORE, THE MODEL IS CONSIDERED APPROPRIATE FOR SIMULATING GROWTH, DEVELOPMENT AND YIELD OF MAIZE UNDER 4 LEVELS OF NITROGEN FERTILIZER. IN THIS CASE, IT IS RECOMMENDED THAT THE MODEL IS CALIBRATED AND VERIFIED, AND THEN, IT IS APPLIED FOR RESEARCH PURPOSES IN KARAJ CLIMATIC CONDITIONS.