The invention provides a method for determining the content of chloroformyl in a chloroformyl compound, which comprises the following steps: adding excessive alcohol and an unsaturated nitrogen-containing heterocyclic compound in sample solution containing the chloroformyl compound to be determined for carrying out reaction; and further utilizing the excessive silver ions to be reacted with chlorine ions, then determining the concentration of the chlorine ions by titrating the residual silver ions, and finally calculating the content of the chloroformyl according to the concentration of the chlorine ions. The determination method has simple operation and low cost, and the color change at the end point of titration is obvious.