The present invention relates to the technical field of 
polymer material preparation, and especially to an air-
drying unsaturated polyester resin for an easy-
polishing gel coat, and a preparation method thereof. The resin is prepared by the following steps, wherein the steps comprise that: an organic 
polyol and a renewable 
vegetable oil are subjected to an ester exchange reaction, and then are subjected to a condensation 
polymerization with a 
small molecule dihydric 
alcohol or a 
dibasic acid, tetrahydrophthalic anhydride and allyl 
ether; the formed 
polymer is dissolved in 
styrene to prepare the resin. The air-
drying unsaturated polyester resin of the present invention has the following advantages that: (1) the renewable 
vegetable oil is selected as the main component, such that the use of the toxic and harmful 
chemical engineering raw materials is reduced so as to meet the green 
environmental protection concept; (2) the 
vegetable oil, the tetrahydrophthalic anhydride, the allyl 
ether and the like in the resin component provide good air-
drying properties, such that the resin can be widely applicable for the fields with high air-drying requirements. The resin of the present invention is mainly applicable for the easy-
polishing gel coat with the high air-drying requirements, and has characteristics of excellent 
toughness, excellent adhesion, excellent 
weather resistance, excellent 
polishing property and the like. In addition, the resin of the present invention has good air-drying property, and the gel coat prepared by the resin of the present invention has characteristics of good adhesion, low 
porosity, easy polishing and the like.