Methylene blue, also known as methylene blue, is mainly used clinically in patients with nitrite poisoning. Nitrite poisoning, also known as enterogenic cyanosis, causes the body’s ferrous hemoglobin to oxidize to methemoglobin and lose the ability to combine with oxygen due to the body’s intake of nitrite, resulting in the body’s symptoms of severe hypoxia. The patient shows a series of symptoms such as cyanosis of the lips and mouth, cyanosis of the extremities and hypoxia, which can be treated with methylene blue. Because methylene blue can reduce methemoglobin to ferrous hemoglobin, restore the ability to combine with oxygen and restore the body’s oxygen supply, so the main role of methylene blue is to treat methemoglobinemia caused by various reasons, especially those caused by nitrite. At the same time, methylene blue than can be applied to the treatment of cyanide poisoning.