Sputum and croup are two different pathological breath sounds with different production mechanisms and clinical manifestations. 1. Sputum ringing is a special kind of wet rales, which is the vibration of phlegm secretion in the trachea, which is produced during expiration and inspiration, but mainly during inspiration, and will be weakened or even disappeared when the secretion is eliminated or sucked out. 2. Croup is a dry rumble, generally less secretion in the airway, due to the airway mucosa has obvious congestion, edema, bronchial smooth muscle contraction and spasm. The relative narrowing of the airway is obvious, and there is a limitation of ventilation and gas exchange, which may endanger the patient’s life in serious cases. 3. Sputum sound is usually seen in wheezing bronchitis, and croup is one of the important signs for diagnosing bronchial asthma and wheezing chronic bronchitis. It is recommended that patients go to the hospital in time when they experience discomfort, and under the guidance of the doctor to clearly determine the sputum sound and rales, to avoid self-diagnosis errors.