The invention relates to a synthesizing technology and device for improving nicosulfuron purity. The technology is characterized in that 3-[(N,N-dimethylaminocarbonyl)-2-pyridyl] sulfonylcarbamate, 4,6-dimethoxy-2-
pyrilamine and methylbenzene are heated to condense; mixed steam of methylbenzene treated as a
solvent in the reaction and ethyl
alcohol produced in the condensation enters a condenser;the
mixed solution of condensed methylbenzene and ethyl
alcohol enters an absorbent storing tank; methylbenzene absorbed through the ethyl
alcohol is heated through an absorbent, and then the methylbenzene is added to a reaction kettle; the reaction is stopped when the content of the ethyl alcohol in the mixed steam produced by the reaction kettle is less than 0.0005%; the
mixed solution in the reaction is cooled and centrifuged to obtain nicosulfuron. According to the technology, the ethyl alcohol produced in the reaction can be quickly and effectively removed, and the reaction is promoted to forwards perform, thus the purity and the yield of nicosulfuron can be improved; and moreover, the methylbenzene treated as the
solvent and taken out through the ethyl alcohol is recycled, so that more energy is saved; and the reaction cycle is greatly reduced through the design, and as a result, the production efficiency is improved.