The causes of yellowish-green mucus in the eyes of 4-year-old children include conjunctivitis, dacryocystitis or dacryoadenitis, etc., which can be treated clinically with medication or surgery. 1. Conjunctivitis: mainly due to microbial infections, the patient may not only show the symptoms of yellow-green mucus in the eyes, but also may be accompanied by conjunctival congestion, pre-auricular lymph node enlargement, etc., clinically can be treated by tobramycin eye drops and other drugs. 2. Dacryocystitis: mainly caused by pneumococcus, streptococcus, staphylococcus and other infections, the patient’s symptoms can be manifested as eye secretion of yellowish-green mucus, swelling of the lacrimal sac area, and so on, clinically can be taken to nasal lacrimal sac anastomosis, lacrimal sac removal and other ways of treatment. 3. Dacryoadenitis: mainly due to bacterial infection, the patient may manifest as elevated body temperature, headache or eye secretion of yellow-green mucus, etc., can use levofloxacin eye drops or tobramycin eye drops for treatment. There are many other causes of yellow-green mucus in the eyes of 4-year-old children, and it is recommended that they go to the hospital in time and do not use their own medication.