After the Japanese surrender in 1945, he was an important commander in the Chinese Civil War serving under Du Yuming and Chen Cheng in Manchuria.

Zheng was conservative with respect to Chinese cultural traditions of filial piety, which was recognized by other Neo-Confucians like Chiang Kai-shek.

During his time in Whampoa, he served as the party representative of the Fourth Company of the Second Battalion within First Regiment of the National Revolutionary Army.

[4] In November of the same year, he was promoted as commander of the Eighth Regiment and advanced towards Chinese coastal provinces of Zhejiang and Jiangsu.

[5] In August 1927, he served as the chief of staff of the Xuzhou Garrison Command and was later transferred to as head of the Ninth Army Training Corps.

[10] In March 1938, he led his troops to participate in the Battle of Taierzhuang, and together with friendly forces, he defeated the Seya Detachment of the 10th Division of the Imperial Japanese Army.

Later, he was promoted as commander of the newly formed 11th Army and after participating in the Battle of Zaoyang–Yichang, he took on the defense mission of the area west of Yichang and north of Yidu in Hubei.

In April 1944, the reinforced Chinese Expeditionary Force along with US Army's Merrill's Marauders began to attack Myitkyina.

On October 16, the Chinese Expeditionary Force in India continued its offensive and captured Bhamo in northern Burma on December 15.

[18][19] In Yunnan, Zhang was considered popular with his troops, and many of the soldiers recruited and trained there would remain with him throughout the remainder of his campaigns with the Kuomintang.

It is during this time that Zheng came under the command of General Du Yuming, and himself gained a degree of notoriety inside China.

At the Sixth National Congress of the Kuomintang in June 1945, Zheng was elected as an alternate member of the Central Executive Committee.

[22] On December 24, he flew back to Shenyang and in January 1948, he served as deputy commander-in-chief of the newly established 'Northeastern Bandit Suppression Headquarters' [zh].

In March, he concurrently served as commander of the First Corps and chairman of the Jilin Provincial Government, and led his troops to defend Changchun.

Chiang also attempted to keep the city supplied by air-drops, but the Nationalist air force was unable to fulfill this role due to its small size and lack of experience.

After destroying or thwarting several Nationalist relief columns, communist troops made overtures to the defenders, enticing them to surrender, but these were unsuccessful.

Famine was used by the communists during the siege in order to force the defending nationalist troops to capitulate; estimates range as high as 330,000.

Only Zheng Dongguo's Corps Headquarters and the Special Forces Regiment held on to the Central Bank Building in the city.

[28] The Corps' Deputy Chief of Staff General Yang Youmei [zh] contacted the People's Liberation Army and proposed resistance for one or two days before surrendering.

[31] In his later years, Zheng stated in several interviews that he regretted holding out for so long in Changchun, believing that it only caused further suffering and death.

In 2006, during the Qingming Festival, Zheng's relatives moved his ashes from Babaoshan and placed it in a tomb at the southern foot of Jiashan Mountain in Shimen County.

[30] In 1918, at the age of 15, Zheng's father arranged for him to marry Tan La'e, a family girl from same village who was eight years older than him.

[33][34] In the 1991 Chinese epic war film Decisive Engagement: The Liaoxi-Shenyang Campaign, he was potrayed by actor Shi Jing.