The cotton fabrics (CF) with durable and stable antibacterial function is very important in the field of medicine and public health, and it is still a challenge to explore highly efficient antibacterial materials. Herein, by using one‐pot method of soap‐free emulsion polymerization, a kind of polymer cationic broccolo‐shaped nanoparticles (PCBsNPs) with antibacterial activities was synthesized, and applied to coating CF, which afforded PCBsNPs coating CF (PCBsNPs@CF). It was characterized by Fourier transform infrared microspectroscopy, scanning electron microscopy, dynamic light scattering, X‐ray photoelectron spectroscopy and contact angle test. Their antibacterial efficiency against gram‐positive and gram‐negative bacteria was studied. It indicated PCBsNPs@CF presented efficient and long‐lasting antibacterial activities, and could effectively restrain bacterial adhesion. Its antibacterial and bacterial anti‐ adhesion mechanism was illustrated. Hence, PCBsNPs@CF had great application potential as clothing, medical dressings and home textiles.