Normal human ki-67 is negative, breast cancer ki-67 less than 14% is low expression, Ki-67 more than 14% is high expression, different laboratory criteria can be different. Ki-67 is called proliferation index, which can be used as one of the evaluation criteria for the malignancy degree of breast cancer, together with estrogen receptor ER, progesterone receptor PR, proto-oncogene HER2 and other pathologic indicators. According to the latest standard, the judgment value of high and low expression of Ki-67 is usually 20%~30% as the threshold, and higher than this level is considered high expression and lower than this level is considered low expression. However, it is more customary to refer to Ki-67 over 14% as high expression and Ki-67 less than 14% as low expression. Ki-67 proliferation index plays an important role in the design of treatment plan and prognosis assessment, such as high expression of tumors with high risk of metastasis and recurrence, which requires high attention. Normal people are negative for Ki-67, if the index is positive, it is recommended to go to the hospital in time.