When there is involuntary flow of yellow water from the nose, clinically it is mainly seen in maxillary sinus cysts. The main cause of maxillary sinus cysts is recurrent rhinitis, colds and sinusitis that cause mucosal and submucosal fluid accumulation in the sinuses, followed by the formation of cysts, which do not cause any symptoms when they are small. When cysts are small, they do not cause any symptoms. When cysts gradually increase in size, they can cause headache, nasal discomfort, nasal congestion, runny nose, and yellow water in the nose. When the body position changes or strenuous exercise, the cyst wall becomes thin and the cyst wall ruptures. The cystic fluid will flow out from the middle nasal passage of the maxillary sinus opening, followed by the symptoms of yellow nasal discharge. In this case, further CT examination of the sinus is needed at the hospital, and if the diagnosis of sinus cyst is confirmed, sinus cyst removal can be performed under sinus endoscopy.