The CANDY model describes important processes of C and N cycle of the unsaturated zone for example nitrogen leaching and ground water formation. Objects of the simulation are geographical units, equal the input data: climate, soil and landuse. This homogeneity affects the result of simulation: the model output is described by fixed numerical values while parameters in real systems shows fluctuations. The poster demonstrates a method which describes the effects of uncertainties in model input on model output nitrogen leaching and ground water formation. There are shown the problem definition, problem solution and a concrete example: an application of the Loess-Chernozem zone in East Germany.