In order to study the preservation effect of oregano essential oil in plastic films, oregano essential oil, as an antibacterial agent, was added into ethylene-vinyl alcohol copolymer (EVOH) and polyethylene (PE) respectively, then the food preservative films were prepared by extrusion casting. The mechanical properties, transmittance and haze of the preservative film were characterized. The snakeheads were then packaged in the preservative films, and the changes in drip loss rate, pH, thiobarbituric acid (TBA) and total viable count over time were determined. The results showed that the addition of oregano oil has little effect on the basic properties of the film; the preservative films could slow down the growth rate of drip loss rate and pH of the packaged snakeheads pieces and inhibit the lipid oxidation of fish. The total viable count in the blank group of fish samples in this experiment reached almost 6 lg CFU/g on the 4th day, while the total viable count in the sample group containing essential oils was close to 6 lg CFU/g on the 8th day. According to the change of the total viable count, relative to the blank group, the preservative films containing essential oil could slow down the growth rate of microorganisms in the packaged fish meat.