Ammonia (NH3) volatilization is an important pathway in soil N cycling and often responsible for the low efficiency of N fertilizer in plant-soil systems. In the North China Plain, NH3 volatilization accounts for up to 50% total N applied in the field. NH3 volatilization is strongly influenced by soil and climatic factors and management practices, and measuring NH3 volatilization is also a costly and time consuming exercise. A NH3 volatilization sub-model was developed under the simulation framework of WNMM for the intensive wheat-maize cropping system in the North China Plain. A unique feature of this simulation component is the introduction of the fertilizer N distribution function in soils for different applying methods: surface broadcasting (SB), surface broadcasting followed by irrigation (SB+I) and deep placement (DP). This sub-model calculates NH3 volatilization from surface and subsurface soil separately. For the surface layer, NH3 volatilization is controlled by soil temperature and wind speed, while for the subsurface soil layer, it is regulated by soil temperature, soil moisture, CEC and depth. The reason of not considering pH impact is that the pH value for the surface soil in the North China Plain is quite uniform and high (pH> 8.5). The NH3 volatilization sub-model of WNMM satisfactorily simulated NH3 volatilization from soils under different application methods (SB, SB+I and DP) during wheat and maize growing seasons, compared with the field measurements by micrometeorological technique carried out in 1998-1999 at two sites in the North China Plain. The DP and SB+I significantly reduce NH3 losses comparing to the SB. The NH3 volatilization accounted for 48% of applied urea in SB compared to 11 and 18% for the DP and SB+I, respectively, in the irrigated maize.