A carboxymethyl chitosan fruit fresh-keeping coating agent in the technical field of food engineering and a preparation method thereof. The fresh-keeping coating agent is: 0.5%-4% of carboxymethyl chitosan, 0.1-1% of glycerin, 0.3-2.4% of Tween 80, 0.1-1% of DL-α-tocopheryl acetate, 92% of water -99%. Heat water in a water bath to constant temperature, add carboxymethyl chitosan, stir until completely dissolved, then add glycerin, stir well with Tween, then add DL-α-tocopheryl acetate and stir until completely dissolved, let it sit at room temperature Cooling, followed by filtering to remove undissolved substances, degassing under vacuum, standing overnight at room temperature, degassing again under vacuum, standing at room temperature, and obtaining carboxymethyl chitosan fruit fresh-keeping coating agent. The fresh-keeping coating agent of the present invention is coated on the surface of fruits by soaking or spraying to form a fresh-keeping film and maintain the quality of the fruits during storage.