The invention provides a rosin-based fruit and vegetable fresh-keeping coating agent and a preparation method of the rosin-based fruit and vegetable fresh-keeping coating agent. The preparation method comprises the following steps: 1, performing D-A addition reaction on rosin, namely, heating 100 parts of rosin to about 160 DEG C to melt, adding 5-30 parts of unsaturated acid or anhydride under stirring, keeping the temperature to 180-220 DEG C, reacting for 1-4 hours to obtain a rosin addition product; 2, performing moderate esterification reaction, namely, slowly adding 5-20 parts of polyol and 0.2 part of nano ZnO catalyst in 100 parts of prepared rosin addition product, keeping the temperature to 200-230 DEG C, reacting for 1-6 hours to obtain a rosin esterification product; and 3, post-treating, namely, introducing saturated water vapor in a reaction kettle filled with the rosin esterification product, continuously blowing and steaming for 1-3 hours, then removing water and low-boiling point neutral products in the esterification product through vacuum decompression to obtain a coating agent product. The rosin-based fruit and vegetable fresh-keeping coating agent can be well soluble with alcohol, and is good in gloss durability and weather resistance.