Abstract: Several challenges of scaling-up that arise when applying crop simulation models developed for the plot-scale leve1 or the field-scale level to broader spatial scales and higher system levels are systematically summarized．These problems include the variability of environmental variables in space and time，the spatial aggregation of response，spatial average bias，temporal variability bias and bias occurring because of neglecting new properties and processes in the existing models．Some potentially useful approaches for controlling and minimizing these errors are concluded．