The invention relates to a malononitrile synthesis method and belongs to the technical field of malononitrile synthesis. The malononitrile synthesis method comprises the following steps of 1, adding methanol or ethanol into a reactor, feeding ammonia gas into the reactor at a temperature of -20 to 50 DEG C, dropwisely adding methyl cyanoacetate or ethyl cyanoacetate into the reactor at a temperature of -20 to 50 DEG C, after dropwise addition, carrying out heat-preservation stirring, carrying out reduced pressure degasification until a temperature is reduced to below -10 DEG C and carrying out filtration and drying to obtain cyanoacetamide, and 2, mixing a dehydrant, a catalyst, cyanoacetamide and a solvent, heating the mixture for a reflux reaction lasting for 6h, carrying out cooling and filtration, removing the solvent to obtain a crude product, and carrying out reduced pressure rectification to obtain a malononitrile product. The preparation method has less reaction processes, can be operated simply, has a high yield and good product purity, utilizes cheap and easily available raw materials, greatly reduces a production cost, is free of an adsorbent, has a less phosphorous oxychloride use amount, greatly reduces three wastes, realizes easy recovery and recycle of the solvent, is suitable for industrial production and solves the problems of the existing a malononitrile synthesis method.