Chitosan-tarragon essential oil nanocapsules were prepared by ion gelation method. The effects of the mass ratios of tarragon essential oil to chitosan, pH of chitosan solution, and the mass ratio of sodium tripolyphosphate to chitosan on the encapsulation rate of tarragon essential oil nanocapsules were investigated. Box-Behnken experiment design and response surface analysis were used to optimize the preparation process of nanocapsules, and the quadratic regression model was established. The results showed that the optimum preparation process of tarragon essential oil nanocapsules was the mass ratio of tarragon essential oil to chitosan 2∶1, pH=3.5, and the mass ratio of sodium tripolyphosphate to chitosan 0.4∶1.0. The encapsulation rate of chitosan-tarragon essential oil nanocapsules was 43.67%. Fourier infrared spectroscopy analysis confirmed that tarragon essential oil was successfully encapsulated. Transmission electron microscope (TEM) analysis showed that the nanocapsules were relatively regular circles with an average particle size was about 40 nm. Differential scanning calorimetry analysis showed that the tarragon essential oil nanocapsules had good thermal stability.