Chang Chun-sung graduated from the 1st Class of the Whampoa Military Academy.
Lt.-Gen. Chang Chun-sung first served as a battalion commander under General Chen Chi- tang (then Commander of Kwangtung 11th Division) and participated in the campaign against General Chen Chiun-ming in the East River region for this service, he was promoted a regimental commander of the Canton Garrison Force. Then he joined the 19th Route Army in Kiangsi in 1930 and commanded the 6th Regiment of 78th Division of the Army.
When the 19th Route Army was transferred from Kiangsi to Shanghai-Nanking Area, he was assigned the garrison of Chapei in Shanghai with headquarters T ear the Shanghai North Railway Station. Upon the outbreak of Japanese hostilities in Shanghai on January 28, 1932, he was the first officer in the Army to offer active resistance and fought against the Japanese marines for the first week, successfully holding the Japanese advance in check. Owing to the heavy casualties suffered by his regiment during the severe engagement, his regiment was transferred to the rear for rest and reorganization but was again sent to the Kiangwan front where he effectively blocked the Japanese advance and inflicted heavy casualties on them on several occasions.
When the main body of the 19th Route Army retired from Shanghai to Soochow, his regiment covered the withdrawal of the Army in Kiangwan. After the army was transferred to Fukien following the conclusion of the War, Chang Chun-sung was promoted Commander of 156th Brigade of the 78th Division, succeeding the well-known defender of Woosung, General Oung Chao-wan. When the Fukien Independence Movement broke out in 1934, he was made an Army Commander, but after the collapse of the Movement, he was relieved of his duties and came to Nanking to enter the Central Military College for further training.