The work aims to prepare a new antibacterial polyvinyl alcohol composite film with good mechanical and antibacterial properties. Cellulose nanocrystals were prepared by acid hydrolysis, dialdehyde cellulose nanocrystals were prepared by oxidation of sodium periodate, and silver-dialdehyde cellulose nanocrystals (Ag-DCNC) were in-situ synthesized by incorporation of Tollens' reagent. With PVA as the film base, the composite film (Ag-DCNC/PVA) made of Ag-DCNC and polyvinyl alcohol (PVA) was prepared by solution casting. The tensile strength of composite films with 3% (volume fraction) Ag-DCNC content was improved by 8.8% compared with the pure PVA films. The antibacterial effect of composite films with 5% (volume fraction) Ag-DCNC content on escherichia coli and staphylococcus aureus was better. Ag-DCNC/PVA composite films show good mechanical strength and antibacterial effect against two kinds of bacteria. With both good properties and simple synthesis technology, such material can be treated as a very promising antibacterial film applied in the packaging industry.