ObjectiveTo analyze the causes of occupational acute 1,2-dichloroethane (1,2-DCE) poisoning accident during the use of polyurethane grouting materials for waterproof plugging operation in the construction industry. Methods By combining the clinical symptoms of the patient, worksite survey of occupational health and workplace occupational hazards monitoring method, the cause of an occupational acute 1,2-DCE poisoning accident was investigated at a construction site during the use of polyurethane grouting material for waterproofing and plugging operations. Results The patient was engaged in waterproof grouting work using polyurethane grouting material. The main volatile organic components in the raw materials were 1,2-DCE, with traces of dichloromethane, methyl acetate and others. The result of post-incident on-site investigation showed that the short-term exposure concentration of 1,2-DCE in the workplace air was 578.70 mg/m³, which was more than 30 times higher than the national occupational health standard limit. The mass concentration of 1,2-DCE in the patient's blood was 230 μg/L. Combined with the patient's occupational hazard exposure history, clinical manifestations, worksite survey of occupational health, and laboratory test results, according to GBZ 39-2016 Diagnosis of Occupational Acute 1,2-Dichloroethane Poisoning, this incident was diagnosed as a severe occupational acute 1,2-DCE poisoning event caused by the use of inferior polyurethane grouting material. Conclusion The excessive concentration of 1,2-DCE in the workplace air is the main cause of this poisoning accident. Construction sites with confined space operations should improve various occupational health management systems, occupational health engineering protective facilities, and personal protective equipment must be provided for workers.