As one necessary step for a good modeling, this study was aimed at analyzing the sensitivity of GreenLab model for maize. When instantaneous value of biomass generation is considered as the output, the system tends to be linear, the level is above 94% in SRC(Standardized Regression coefficients)study. Conversion efficiency and characteristic surface are proved to be the most sensitive factors. In Sobol's measure, we excluded the two most sensitive factors in the analysis, then the system linearity tends to be weaker and we got the detailed sensitivity indexes for the other uncertain parameters, by which we get the clearer driven force of maize growth in different stages.