Sputum culture examination is mainly used for bacteriological examination of respiratory tract infections, sputum culture results negative may have the following reasons: 1, the patient’s sputum itself does not have bacterial infection, culture 7 days after the report can show sputum culture results are negative. 2, when doing sputum culture, the patient has used antibiotics before, antibiotics lead to sputum culture pathogenesis produce false negative, that is, itself has infection but not able to sputum culture In this case, treatment should be based on clinical experience and the infection should not be considered as not fully controlled. 3, sputum culture negative, if it is in patients with tuberculosis infection is not easy to culture, tuberculosis bacteria do sputum culture has very high requirements. So a negative sputum culture at least indicates that there is no common respiratory bacterial infection at the moment, but it does not mean that the infection is under control, and the decision to use targeted antibiotics should be based on the treatment of the condition that has passed, and the patient’s main symptoms.