The invention relates to a flooded lead-acid storage battery electrolyte impurity detection method, and belongs to the technical field of lead-acid storage battery electrolyte. According to the flooded lead-acid storage battery electrolyte impurity detection method, an electrolyte to be detected is mixed with a stabilizing agent A and a color developing agent B in storage battery application field, and comparison with a standard mixed solution or a color gradation card is carried out so as to determine the content of copper ions in the storage battery sulfuric acid solution; the stabilizing agent A is a mixed solution of nitric acid and a water soluble fluoride salt; and the color developing agent B is a mixed solution of bis(cyclohexanone)oxaldihydrazone or dithiooxamide, and a water soluble diethyldithio amino organic acid salt. The flooded lead-acid storage battery electrolyte impurity detection method can be used for sampling and detection on storage battery application field, operation is simple, no professional operation staff or precision equipment is needed, detection time is short, and detection accuracy is high.