Add a sodium cyanide aqueous solution with a mass concentration of 30% and a mass of 91.0g to the reaction flask, and then add 93.0g of 2,4-dichlorobenzyl chloride (obtained from the pre-operation), 150 ml of dichloroethane and 1.5 g of the phase transfer catalyst tetrabutylammonium bromide, the temperature was raised to 70°C, and the reaction was kept for 5h.After the reaction was completed, it was extracted twice with 100 ml of dichloroethane. After drying, it was distilled and rectified to obtain a total of 75.5 g of 2,4-dichlorobenzeneacetonitrile. The yield was 88.1% and the GC purity was 99.2%.