The invention discloses an edible mushroom fresh keeping agent and a preparation method thereof. The edible mushroom fresh keeping agent is prepared from the following components: sarcodon quel fruiting body enzyme extraction liquid, dictyophora echinovolvata fruiting body enzyme extraction liquid and chitosan in the weight ratio of the sarcodon quel fruiting body enzyme extraction liquid, to the dictyophora echinovolvata fruiting body enzyme extraction liquid and the chitosan being 0.5-2:0.25-1.25:0.5-1.5. The preparation method comprises the following steps of uniformly mixing the sarcodon quel fruiting body enzyme extraction liquid, the dictyophora echinovolvata fruiting body enzyme extraction liquid and the chitosan so as to obtain a target edible mushroom fresh keeping agent. The edible mushroom fresh keeping agent disclosed by the invention is safe, non-toxic, edible, good in antiseptic effect, and long in fresh keeping time. Agaricus bisporus painted with the edible mushroom fresh keeping agent disclosed by the invention for keeping fresh, is stored in the environment of 8-12 DEG C, and after being stored for 9 days, the color, the hardness, and the mouth feel of the agaricus bisporus are not changed basically. Bolete painted with the edible mushroom fresh keeping agent disclosed by the invention, for keeping fresh, is stored in the environment of 1-3 DEG C, and after being stored for 19 days, the hardness and the mouth feel of the bolete are changed little. The edible mushroom fresh keeping agent disclosed by the invention is used for fresh keeping of edible mushrooms, so that the depletion of products is greatly reduced, and the sale benefits are increased.