A sudden death warning method, device and system. The method comprises: 1. physiological information extraction and detection; extracting and detecting breath, oxygen saturation, heart rate, and heart rate variability information of a test object to obtain six monitoring indicators of respiratory rate, AHI, arterial oxygen saturation, heart rate, and Poincare map indexes SD1 and SD2; 2. physiological information exception detection; performing exception detection on the physiological information obtained in step 1 and calculating a warning level; during the exception detection, executing step 3 if the result is abnormal; continuing detection if the result is normal; 3. acoustic, light and vibrating alarm; driving an alarm to give out sound, emit, and vibrate, and provide the corresponding alarm level. The higher the alarm level is, the higher the sudden death risk is. When the alarm level is greater than 3, a doctor is required. When the alarm level is greater than 5, an emergency is required. The device comprises a breath sensor module (1), an oxygen saturation sensor module (2), a heart rate sensor module (3), and a microprocessor module (4).