The invention discloses a method for detecting the content of corrosive chlorine in phosphate fire-resistant oil. The content of corrosive chlorine in the phosphate fire-resistant oil is accurately calculated through decomposing and separating the corrosive chlorine from the phosphate fire-resistant oil. According to the method, the defects that only the content of total chlorine can be detected and the corrosivity of new oil and running oil of the phosphate fire-resistant oil cannot be evaluated in a targeted manner in an existing method are overcome; accurate detection of the content of corrosive chlorine in the phosphate fire-resistant oil is achieved; easy-to-degrade and hazardous fire-resistant oil is effectively prevented from entering equipment; whether an oil product is polluted by corrosive chlorine or not in the use process is accurately judged; and the operating security of the equipment is ensured.