The invention belongs to the field of toluene diisocynate production technology and relates to a dehydration method during the production process of toluene diisocynate. Toluenediamine and phosgene have cold light gasification reaction to obtain a mixture flow of carbamyl chloride, amidogen hydrochloride and hydrogen chloride; the mixture flow flows into a phosgenation reaction tower; carbamyl chloride and amidogen hydrochloride react to produce toluene diisocynate and the by-product hydrogen chloride; at the bottom of a hydrogen chloride rectifying tower, the mixture flow of amidogen and hydrogen chloride is divided into two parts, most of the mixture flow returns to the top of the phosgenation reaction tower and serves as the backflow, and the rest of the mixture flow enters into a drain sump containing activated carbon as the catalyst; water and phosgene in the mixture flow react to produce hydrogen chloride and carbon dioxide to remove water in the mixture flow under the function of the activated carbon catalyst; the dehydrated mixture flow enters into the bottom of the phosgenation reaction tower for further rectification and is discharged from the bottom of the phosgenation reaction tower for next step. The dehydration technology is simple and environmentally friendly, the cost is low, and the dehydration effect is excellent.