Abstract: Before the Opium War, the relation between the Qing Dynasty and Western countries was replete with conflict, especially in judicial administration. The Qing Dynasty adapted some unusual judicial principles for specific political purposes, especially the principle of ‘a life for a life’ in criminal cases, which caused a lot of trouble between China and the West and ultimately became a primary cause of increased diplomatic conflicts and wars. This paper will discuss the applications of ‘a life for a life’, its characteristics and its actual effects, to expose this principle’s substantial influence on the diplomatic relations between China and West.