In the War of Resistance against the Japanese Aggression,the Eighth Route Army persisted in the guerrilla warfare behind the front line and this was crucial for them to get stable sources of ammunition. Their four major sources of ammunition were spoils of war,manufacturing,collection and purchase from civilians,and supplies from the Nationalist government. In different stages of the war,the contributions from the four sources also varied. In general,in the early stage,the Eighth Route Army obtained more ammunition than they used,while in 1941-1942,they used more than they obtained. After 1943,with efforts in many ways,the stocks of their ammunition increased again. The complicated sources and endeavor of the Eighth Route Army to obtain ammunition demostrated the backdrop of the United Front in the War of Resistance,and also showed the extremely strong ability of the Communist Party of China in social mobilization and implementation,as well as their flexible policies and strategies.