Depending on the symptoms, phlebitis is categorized into 4 grades, most of the phlebitis is not clinically manifested and these are collectively known as grade 0. If there is just a vein going around the area, the skin is red and there is not necessarily a symptom of pain it is categorized as grade 1. If the veins appear red and swollen with pain, such phlebitis is categorized as grade 2. In addition to the symptoms of grade 2, the presence of a palpable nodule in the area of the inflamed veins is classified as grade 3. Striated nodules exceeding 2.5 cm and the presence of localized red and swollen areas of skin oozing with infected pus can be classified as grade 4. And the classification is mainly 4 categories: 1, mechanical: established on the basis of the theory of vascular wall injury, repeated intravenous injection of patients, caused by vascular wall injury. 2, chemical: to the vascular wall irritation of the drug injection, caused by the intima-media reaction of the vascular wall caused by, especially chemotherapeutic drugs. 3, bacterial: in the invasive operation, due to the disinfection is not complete and other factors, will be the bacterium through the puncture site, and brought into the intravascular. 4, thrombosis: due to local thrombus, resulting in blood transportation obstacles toxic substances can not be metabolized, and the secondary formation of inflammation.