The main difficulty in seismic full-waveform inversion is the strong nonlinearity, which is caused by the complexity of seismic wave propagation. The analysis of the behavior of the objective function variation with the parameter perturbation scale can help us to choose the reasonable inversion method and strategy. According to Jannaners method to analyze the objective function behavior, the relationship between the objective function calculated by different seismic data subset and the parameter perturbation scale is studied, especially the nonlinearity. The analysis results will provide some theoretical guidance for FWI to implement the multi-step and multi-scale inversion strategy.