Load capability has become the bottle-neck in the progress of high-power solid-state laser facility, the research of which is mainly focusing on the interaction process of laser near-field and optics. Evolvement of experimental near-field intensity with the rise of laser intensity in a multiple-pass amplification laser driver has been researched by power spectral density (PSD). It is shown that, the near-field show obvious frequency-related characteristics, and two-dimensional PSD of near-field is isotropic. Modulation of near-field is due to small-scale self-focusing in high-intensity state. Growth of spatial frequency from PSD curve is mainly in the spatial frequency band, which is decided by the cut-off frequency of spatial filter pinhole.