March of the Volunteers is the theme song of that movie.

March of the Volunteers was originally the theme song created by Nie Er in 1935 for the feature film "Children of the Storm" filmed by Shanghai Dentsu Company. This film tells the story of China intellectuals, represented by the poet Xin Baihua, who joined the army in the early 1930s and went to the anti-Japanese front to kill the enemy heroically to save the motherland. It appeared twice in the film and left a deep impression on the audience. Therefore, it soon became the most famous anti-Japanese war song in China. After the founding of New China, it was designated as National Anthem of the People's Republic of China (PRC) and later officially designated as National Anthem of the People's Republic of China.