Angulation of the common bile duct caused by traction during laparoscopic cholecystectomy is one of the leading causes of iatrogenic bile duct injury. The mobility of the common bile duct refers to its flexibility for lateral swing and vertical stretching. Based on long-term clinical experience, the author classifies the common bile duct into two types: fixed type and lax type. The fixed type has poor mobility and is not prone to traction-induced angulation. In contrast, the lax type possesses considerable mobility and is easily angulated under traction, which may lead to common bile duct injury due to improper clipping and transection. Close vigilance against the lax common bile duct with high mobility is of great clinical significance for preventing iatrogenic bile duct injury and ensuring surgical safety.