From the autumn of the second year of Jianyan (1128) to the spring of the third year, the Jin army attacked the Song Dynasty again, and the vanguard pointed directly at Yangzhou. Zhao Gou, who was still "patrolling" in Yangzhou, hurriedly abandoned the city and fled to Hangzhou. At this time, Miao Fu and Liu Zhengyan staged a coup d'état and forced Zhao Gou to abdicate.
At that time, Zhang Juntun was in Wujiang County (now south of Wuxian County, Jiangsu). Among the generals, Zhang Jun is already quite prestigious. In order to stabilize the coup situation, Miao Fu and others issued an edict to crown Zhang Jun as the commander of the four compartments of the Japanese and Tianwu, but Zhang Jun refused to accept it. At this time, the three armies were raging, and Zhang Jun announced to everyone: "This matter should be decided by Zhang Shilang (that is, Zhang Jun, who was previously a waiter of the Ministry of Rites)." "The military spirit is decided. Zhang Jun then led 8,000 people to Pingjiang (now Suzhou, Jiangsu) to meet Zhang Jun. Zhang Jun recounted the coup d'état to Zhang Jun in detail, and burst into tears. Zhang Jun was quite valued by Zhao Gou after Queen Qin of Xiangzhou, and at this time he saw Zhang Jun so loyal to the imperial court, and was moved by it, and expressed his loyalty to Zhang Jun while shedding tears, and raised troops to ask Miao and Liu for their crimes. At this time, Han Shizhong, Lu Yijie, and Liu Guangshi came to the meeting and agreed to discuss Miao and Liu together. So Zhang Jun spread the word to China and abroad, denounced the crimes of Miao and Liu, and ordered Zhang, Han, Liu, and Lü to rebel. The armies of Zhang and Han fought fiercely with the Miao Fu army, and the Miao Fu army was defeated and fled. Zhang Jun, Han Shizhong, Liu Guangshi, and Lu Yihao entered the city and met with Gaozong Zhao Gou in the inner hall. Gaozong praised the generals one by one, and then ascended the throne again. Feng Zhang Jun was the envoy of the Zhenxi Army, and the right army in front of the emperor was under control. Later, he was appointed as the envoy of the eastern part of Zhejiang.
Soon Jin Wu 71 led the Jin army to invade the south, and the defense of the river completely collapsed, and the Jin soldiers crossed the Yangtze River and besieged Jiankang. In October, when Gaozong Zhao Gou heard of the collapse of Jiangfang, he hurriedly led the ministers of civil and military affairs to abandon Lin'an (now Hangzhou) and Benming Prefecture (now Ningbo, Zhejiang). Zhang Jun led his army from Yuezhou (now Shaoxing, Zhejiang) to Mingzhou to escort him. The Jin army captured Lin'an, Zhao Gou wanted to continue to flee south, and when he left Mingzhou, he personally gave Zhang Jun the imperial book, and ordered him to lead his troops to resist the enemy in Mingzhou. Soon the Jin soldiers arrived at the city of Mingzhou, and Zhang Jun led the army to meet the battle. Zhang Jun's troops will break the Jin army and kill thousands of enemies. Seeing that the hard attack failed, the Jin army wanted to surrender Zhang Jun, but Zhang Jun categorically refused. Then Zhang Jun considered that the enemy soldiers would come again, so he ordered to clear the wilderness, use light boats to ambush bows and crossbows, and retreat to defend himself. On the first day of the fourth year of Jianyan (1130), the west wind suddenly rose, and the Jin soldiers took advantage of the wind to attack Mingzhou again. Zhang Jun and his retainer Liu Hongdao sat on the tower of the city and sent troops to kill the enemy. Countless Jin soldiers died in the river, so they had to flee at night. After another seven days, the Jin soldiers attacked Mingzhou again. Because the enemy was too strong, Zhang Jun retreated to Taizhou (now Linhai, Zhejiang) in order to save his troops.
After that, Zhang Jun pacified the Jianghuai thieves and was crowned as a captain; Eliminate the puppet Qi regime and be given the post of Shaobao.