In order to solve the undulation defects on the coating of galvanization strips, caused by pressure pulsation of turbulent jet of air knife, LES simulation was conducted on the slit impinging jet under the conditions with and without a guiding jet, respectively. The evolutions of vortex structures of two impinging jets were compared with the numerical fields. Meanwhile, a series of snapshots of impinging pressure fields were extracted for mode analysis via multi-scale Proper Orthogonal Decomposition (mPOD), where the fluctuation power density spectra were studied based on spectral purity, and the spatial modes and coherent structures at the dominant energy spectra were extracted and compared for the two types of jets. Vortex structure analysis shows that the guiding jet promotes the merging of vortices on both sides of nozzle outlet and increases the dominant vortex scale in the flow field. This leads to an increase in the spatial scale of vortex impinging on the wall. Modal and coherent analyses indicate that the guiding jet significantly reduces the fluctuation frequency of impinging pressure on the surface and increase the energy share of the first five modes, resulting in that pressure fluctuation exhibits a significantly low rank characteristic. These findings can help the understanding of wiping process in hot-dip galvanization and improve coating quality.