The invention belongs to the field of adhesives, and particularly relates to a synthesis technique of an alpha-cyanoacrylate monomer, which comprises the following steps: (1) directly reacting cyanoacetate and polyformaldehyde, which are used as raw materials, under solventless conditions by using a basic catalyst; (2) naturally cooling, keeping the temperature, and dehydrating to obtain the crude product; and (3) in the presence of a polymerization inhibitor, preparing the alpha-cyanoacrylate monomer, wherein the basic catalyst in the step (1) is one or mixture of hexahydropyridine, pyridine and KOH, the cyanoacetate is one or mixture of methyl cyanoacetate, ethyl cyanoacetate and n-butyl cyanoacetate, the polymerization inhibitor in the step (3) is hydroquinone and sulfur dioxide, a dehydrating agent is used for dehydration in the step (2); and the dehydrating agent is one or mixture of benzene, methylbenzene and methanol. The reaction process has the advantages of no need of organic solvent, low energy consumption, obvious environmental protection effect and high target product yield.