In recent years, continuous and stable antibacterial ability has received extensive attention in the field of antibacterial composite materials. The researchers expect a kind of antibacterial composites with continuous and stable antibacterial acting and good biocompatibility. Herein we used a unique in-situ modification methods which inspired self-polymerization of dopamine to fix the nano-Ag on the bacterial cellulose (BC). The antibacterial properties of composites were tested in two new methods (antibacterial stability and antibacterial durability). We researched the cause of the antibacterial properties by analyzing the valence state and binding energy of Ag. The chelation between PDA and Ag is considered to the key to stable release of Ag+. The three-dimensional network of BC is also thought to play some role in making Ag+ release stability. Moreover, PDA as a reducing agent, reacting with Tollens reagent to produce nano-Ag nanoparticles, is a good method for reducing the toxicity of nano-Ag and enhancing the biological compatibility of composites. Our results hence illustrate that the BC antimicrobial composites by PDA in-situ reduction nano-Ag has a great potential as an antibacterial dressing with stable antimicrobial properties and biocompatibility.