The development of new antimicrobial drugs is urgently required to overcome bacterial resistance which is a serious threat to human health. Antimicrobial peptides (AMPs) which are ideal substitutes for traditional antibiotics have a unique mechanism of action and do not easily cause bacterial resistance. Herein, a series of new AMPs were designed and synthesized based on the biological characteristics of natural AMPs (such as the positive charge, α-helical structure and amphiphilicity). Biological screening of the AMPs provided an antimicrobial lipopeptide LP21 with efficient antimicrobial activity, serum stability, low cytotoxicity and high membrane-disruptive activity. Besides, LP21 could self-assemble into spherical aggregates in aqueous solutions which encapsulated TC to form LP21@TC nanomedicine, and the encapsulation efficiency was about 50.03 ± 3.03%. More impressively, both LP21 and LP21@TC nanomedicine displayed significant therapeutic effects in vivo, and the LP21@TC nanomedicine could exert a synergistic antimicrobial effect. This work is expected to provide a new research vision for the design of AMPs and synergistic antibacterial sensitization treatment.