The days from the spring of 1941 to 1943 were the most difficult period of the War of Resistance Against Japan in the North China base areas. In the Shanxi-Hebei-Shandong-Henan Border Region, the base areas had been reduced from more than 50 complete counties in early 1939 to seven counties in 1942, when the worst occurred. Some villages in the base areas of southern Hebei were very close to enemy strongholds and bunkers, between which there was no village. The base area in Shandong was seriously encroached upon by the Japanese and the puppet army and by the end of 1942 the area of the base area had shrunk by about one third from that of 1940. In the Shanxi-Chahar-Hebei border area, due to the continuous “sweeping”, “nibbling” and “blocking” of the base by the invading Japanese Army, the troops and civilians in the border area faced the most difficult, arduous and dangerous period since the beginning of the War of Resistance Against Japan. This showed that all base areas behind enemy lines in North China were already facing extremely serious and dangerous living spaces. To reserve this crisis, each base area used the military wisdom, mechanism and strategies of the war of resistance, using the weak to counter the strong, avoiding the solid and striking the weak, and carried out counter-“sweeping”operations with wit, dexterity, bravery but with great difficulty. For example, there were all respectively successful battle cases and miracles of unexpected victories in the process of counter-“sweeping” in the Shandong Anti-Japanese base area, the Jilu-Henan Anti-Japanese base area and the Jin-Cha-Ji Anti-Japanese base area, which showed the dialectical process of mutual transformation and translocation between our inferiority and the enemy's superiority. In the process against enemy's “nibbling away” and “prisoner's cage”, the strategy and tactics of “enemy advancing and us advancing” adopted in the base areas more intensively reflected the accurate application of dialectics. The emergence of armed working teams behind enemy lines made the enemy lines “two worlds a day, the Japanese world in the daytime and the Eighth Route Army world in the evening”. As a result, the enemy's military superiority gradually disappeared, and the base areas behind the enemy gradually passed through the most difficult and dangerous period. By 1944, the base areas in North China were restored and developed. The each base areas overcame the crisis and achieved rapid recovery and development, but also strongly supported the war of resistance on the frontal battlefield, and also played a mainstay role in the lasting persistence and support of the eastern battlefield in the international anti-fascist war.