The cationic antimicrobial peptide GF-17, a 17-mer-derived peptide from human cathelicidin LL-37, has a significant strength in the killing of the methicillin-resistant Staphylococcus aureus and Escherichia coli strains. Herein, we conducted a series of all-atom molecular dynamics simulations to investigate the ability of GF-17 in perturbing the model membranes of the gram-positive, S. aureus, and gram-negative, E. coli, bacteria. We also explored the contributions of the specific residues in the peptide activity. The molecular dynamics results indicated that the peptide is stabilized on the membrane surface and rapidly binds to the phosphate headgroups of the model membranes through the electrostatic interactions and hydrogen bonds. Furthermore, both polar and nonpolar interactions are energetically favored for the binding with the membrane surface. The research also revealed the important roles of the phenylalanine residues in the early insertion of the peptide into the bacterial model membranes. In addition, the results demonstrated that the central residues Arg23 and Lys25 played a critical role in the binding of GF-17 to both gram-negative and gram-positive model membranes, in excellent agreement with experimental studies. This study emphasizes on the pivotal role of basic residues in prompt association of the peptide on the model membrane surface and on the significance of residues Phe17, Ile24, Phe27, and Val32 in hydrophobic interactions. Therefore, our observations provide insights into the membrane-GF-17 interactions at atomic details that are useful to develop potent antimicrobial peptides targeting multidrug-resistant bacteria.