NOVELTY - Synthesizing cytosine comprises mixing 3-cyano-2-ureido-acrylic acid ethyl ester and 2-ureido-ethyl acrylate and then heating and cooling, mixing obtained mixture, 5-ethoxycarbonyl pyridine, alkali and catalyst and then heating, adjusting pH value and drying to obtain 5-ethoxycarbonyl-cytosine, adding hydrochloric acid to mixture, drying mixture and then performing decarboxylation, adding solvent and catalyst into the mixture and then introducing nitrogen gas, and collecting the product.    USE - The method is useful for synthesizing cytosine (claimed).    ADVANTAGE - The method is capable of simply synthesizing the cytosine with high yield of 75.14%.    DETAILED DESCRIPTION - Synthesizing cytosine comprises mixing raw material including 3-cyano-2-ureido-acrylic acid ethyl ester and 2-ureido-ethyl acrylate according to mole ratio and then heating and keeping the temperature for 2-4 hours, cooling the mixture to room temperature, mixing the mixture, 5-ethoxycarbonyl pyridine as solvent, alkali and catalyst and then uniformly stirring, heating the mixture at 60-100 degrees C, keeping the temperature for 2-3 hours and then cooling to room temperature, dissolving the obtained mixture in 4-8 times of water and then adding vinegar acid for acidification to adjust pH value to 7, collecting the solid, washing the solid using acetone and drying to obtain 5-ethoxycarbonyl-cytosine, adding water and alkali into a reaction kettle, uniformly stirring and heating at 70-90 degrees C and then adding 5-thoxycarbonyl-cytosine, keeping the temperature for 10-30 minutes, cooling to room temperature, adding hydrochloric acid to adjust pH value to 5, separating out solid, collecting the solid and washing the solid using water, drying the solid and then performing decarboxylation, adding solvent and catalyst into the solid, introducing nitrogen gas, uniformly stirring the mixture and then heating at 180-200 degrees C, keeping the temperature for 4-8 hours, cooling to room temperature, adding diethyl ether to separate the solid, and collecting the product.