Abstract: Emergency drainage device is an important safety device for floating roof tank to timely drain the overloaded water in case of emergency. In practical application, a large amount of maintenance work is required for the commonlyused float type emergency drainage device with water seal structure. Especially for the float type emergency drainage device in dry weather conditions, frequent water filling is required, and there is potential safety hazard of water seal failure that is difficult to recover. According to the characteristics of PVA and PVDC materials, the solution of a new type of emergency drainage device in composite membrane was designed. Based on its flame retardant modification, PVA was compounded with PVDC, and thereby an emergency drainage device with composite membrane as its main body was designed to make up for the deficiency of float-type emergency drainage device with water seal structure. The field test results show that, since there is no water seal in the composite membrane emergency drainage device of the floating roof tank, the maintenance workload is reduced and the operation safety of the floating roof tank is improved.