The present invention discloses a novel high sealing property unsaturated polyester white primer, and a preparation method thereof. The unsaturated polyester white primer provided by the present invention comprises, by weight, 40-45% of unsaturated polyester PE resin, 0.2-0.3% of an antifoaming agent, 0.3-0.5% of a wetting dispersant, 0.2-0.3% of a polyacrylate leveling agent, 0.1-0.2% of an anti-green agent, 4-6% of organic bentonite pre-clotting slurry, 0.2-0.8% of fumed silica, 3-7% of zinc stearate, 3-9% of 1250 mesh pulvistalci, 7-11% of 800 mesh pulvistalci, 13-21% of ground calcium carbonate, 11-17% of rutile titanium dioxide, 2-5% of a nitrocellulose solution and 1-3% of n-butyl acetate. The unsaturated polyester PE primer provides especially good sealing property for the low density medium density fiberboard, wherein the low density medium density fiberboard is not subjected to a sealing treatment or is treated bad. In addition, the unsaturated polyester PE primer has characteristics of excellent caving resistance, excellent sagging resistance, short polishing time, good polishing property, strong interlayer adhesion, and can be applicable for the comprehensive primer solution schemes for different environments, various processes and plates.