The work aims to obtain chitosan-based composite films with good flexibility and antibacterial ability. Chitosan was firstly reinforced by gelatin and then was plasticized by glycerol to prepare chitosan-based films with good flexibility by means of tape casting. After that, the films were soaked in copper nitrate/sodium hydroxide solution to improve their antibacterial property by in-situ loading nano-CuO particles. The effects of the mass ratio of chitosan to gelatin and the dosage of glycerol on the mechanical properties of the composite films were investigated. Also, the effects of the concentration of copper nitrate on the water vapor permeability (WVP), transmittance and antibacterial property of the composite films were studied. FT-IR and XRD were used to characterize the structure of films. The results indicated that, with the mass ratio of chitosan to gelatin of 5∶5 and the mass fraction of glycerin of 20%, the tensile strength and elongation at break of the composite film were (3.23±0.31)MPa and (159.88±4.14)%, respectively. The concentration of copper nitrate increased, the WVP of chitosan/gelatin/copper nitrate films decreased and then increased, while the transmittance gradually decreased. Moreover, the antibacterial activity of composite films against staphylococcus aureus and escherichia coli was gradually enhanced. With the concentration of copper nitrate of 0.05 mol/L, the optimum WVP and transmittance values of composite films were (30.60±4.02)g•mm/(m2•s•kPa) and (72.61±8.13)%, respectively. When the concentration of copper nitrate was 0.25 mol/L, the film showed good antibacterial ability with the diameter of the inhibition zone for escherichia coli of (27.0±3.0)mm. With the concentration of copper nitrate of 0.30 mol/L, the maximum inhibition zone diameter of the film for the staphylococcus aureus was (26.1±3.1)mm. The chitosan/gelatin films obtained herein have good flexibility and antibacterial property, broadening its potential application in the field of food packaging preservation.