Irrigation, salinity and nitrogen (N) are the three major limiting environmental factors in maize yield potentials especially in arid and semi-arid regions. An integrated water and N Maize Simulation Model (MSM) was modified for salinity conditions using 2009-2010 field experiments data in southwest of Iran. Irrigation levels were: I-1=1.0ET(c)+0.25ET(c) as normal leaching amount, I-2=0.75I(1) and I-3=0.5I(1), salinity of irrigation water: S-1=0.6, S-2=2.0 and S-3=4.0 dS m(-1) and N fertilizer rate: N-1=0, N-2=150 and N-3=300 kg N ha(-1). Data of the first and second year were used to calibrate and validate the modified model, respectively. The MSM model was modified by including the combined effects of water and salt stresses using different water uptake functions. Furthermore, N uptake via mass flow process was also modified. By this modification, the soil salinity was also estimated by the model. Calibration/validation results showed that the water uptake function of Homaee and Feddes led to a better estimation of all parameters than those obtained by other water uptake functions. Based on the NRMSE and d indices, the modified MSM model presented a very good to fair estimation of soil water content, salinity and N, evaporation, transpiration, evapotranspiration, leaf area index, total dray matter, N uptake and grain yield. Besides, under saline irrigation water there was much higher risk to the groundwater contamination by nitrate leaching.