Runny nose is one of the most common symptoms in children, especially after a cold, when the child has a stuffy nose, sneezing and runny nose, clear at first and yellow at the end of the cold. Except for influenza which has characteristic antiviral drugs, most of the colds are viral infections, clear nasal discharge is not considered as bacterial infection and can heal itself, but yellow nasal discharge needs to be treated differently. Under normal circumstances, the nasal mucous membrane in our nasal cavity secretes nasal mucus continuously. Compared with adults, the nasal mucosa of infants and children is more sensitive to various external factors, and the nasal cavity is relatively narrow, so they are more likely to have runny nose. Cold, acute rhinitis, acute and chronic sinusitis, etc. can cause runny nose. In the early stage of cold, the nasal discharge is watery, and then it becomes mucus-like nasal discharge. With the edema of nasal mucosa, the ciliary movement of nasal mucosa columnar epithelium is impaired, the local bacteria in nasal cavity is retained, and the white blood cells swallow the bacteria, the nasal discharge is purulent, yellow-white and cloudy, and as the condition improves, the purulent component decreases and the mucous component increases, and gradually returns to normal. The whole process lasts about 1~2 weeks. If the child is in good spirits and has no fever, it can be cured with local care of the nasal cavity. However, if the baby has yellow thick discharge from the nose and the pus stench is obvious, especially after getting a cold and the course of the disease is more than 10 days, and there is still sticky-purulent nasal discharge, or accompanied by fever and headache, we should consider bacterial infection and sinusitis, and parents should take the baby to the hospital for examination and regular treatment under the guidance of physicians in time, and cannot blindly wait for self-healing. Although children’s runny nose is a common and small thing, but a long runny yellow nose with fever and headache may not be a common cold and cannot wait for self-healing, it is recommended to seek medical treatment in time.