The invention discloses a method for producing metaldehyde, which comprises polymerization of aldehyde under an acidic condition, and is characterized in that: in polymerization, a compound of a general formula XpOnYm is used as a catalyst; in the formula, X may be S, C or P; Y may be F, Cl, Br, I or CN; P may be 1 or 2; n may be 0, 1 or 2; and m is an integer ranging from 1 to 5. Compared with the prior art, the method has the advantages that: a precursor of an acidic catalyst is used as a catalyst; the acidic catalyst is gradually released in a reaction process; and the catalyst is efficient and the reaction time is shorter. In addition, the catalyst used in the invention is cheap and readily available, the use amount is small, the yield of the metaldehyde is improved effectively to 10.2 percent which is higher than the yield that is 6 percent in modern industry; meanwhile, the reaction time is reduced by at least 3 to 10 hours to 30 to 90 minutes from the original reaction time, and thus, the energy consumption for keeping low-temperature environment is reduced greatly. Meanwhile, the method disclosed by the invention is mild in reaction conditions, and the industrialization can be realized easily.