The invention discloses a preparing method of deccox, which uses cheap pyrocatechol as material to obtain deccox products with good quality and low cost by diethoxylation, nitration, alkali hydrolysis, decyloxylation, reduction, condensation, ring closing and hydrolyzation. Compared with the prior art, materials such as 3,4-dihydroxynitrobenzene or catechol ethylether, which are expensive and not easy to buy, are replaced by chemical materials, such as plate caustic soda, pyrocatechol, diethyl sulfate, glacial acetic-acid, nitric acid, glycol monoethyl ether, potassium hydroxide, bromodecane, phosphorus oxychloride, ethoxymethylene, sodium hydroxide, etc., which are cheap and easy to obtain, the reaction condition is gental, the integration cost is 50% lower than that of the prior art.