The invention belongs to the field of high polymer materials, and discloses a cellulose nanocrystal/ethylene-vinyl acetate (EVA) gas separating membrane, a preparation method of the cellulose nanocrystal/EVA gas separating membrane and application of the cellulose nanocrystal/EVA gas separating membrane. The preparation steps of the cellulose nanocrystal/ EVA gas separating membrane comprises (1) adding sodium bromide, a 2,2,6,6-tetramethylpiperidinooxy (TEMPO) reagent and a sodium hypochlorite solution into cellulose nanocrystal suspension liquid, keeping potential of hydrogen (pH) of a reaction to be in alkalinity, adding a saturated salt solution, centrifuging, washing, dialyzing, drying and obtaining carboxylation cellulose nanocrystal; (2) adding the carboxylation cellulose nanocrystal into organic solvent, wherein amine is dissolved in the organic solvent, and then adding a dimethylsulfoxide (DMSO) containing diisopropyl carbodiimide (DIC) and N-hydroxysuccinimide (NHS), stirring, centrifuging, removing upper layer liquid, washing, drying, and obtaining amidate cellulose nanocrystal; and (3) mixing the amidate cellulose nanocrystal and EVA into the cellulose nanocrystal/ EVA gas separating membrane. Due to the fact that the cellulose nanocrystal/ EVA gas separating membrane is good in light transmittance and water-vapor transmission rate, the cellulose nanocrystal/ EVA gas separating membrane has good prospects in food packaging.