As a young girl in rural Imperial China, Mulan is an adventurous and active young girl, at the disappointment of her mother who hopes that she will one day be able to find a husband. Mulan grows up, and is forced to meet with a matchmaker and bring honor to her family. In northwestern China, an outpost is invaded by Rouran warriors, under the leadership of Bori Khan. They are assisted by the witch Xian Lang, who is able to shapeshift to infiltrate the town. Xian Lang transforms herself to appear as a Chinese soldier to report of the attack to the Emperor of China, causing him to issue a conscription decree for one man in each family.
Soldiers arrive in Mulan’s village to enlist soldiers, and her father, Zhou, is forced to volunteer as he does not have a son. Mulan realizes that her elder father will not survive the war, and flees with his armor, horse, and sword to join the army. Mulan arrives at the training camp, which is run by Commander Tung, who had previously served with Zhou in the previous war. Mulan hides her gender and succeeds in training.
Bori Khan’s army continues to advance, causing Tung to end training early and sends his battalion to fight. Mulan chases some of Bori Khan’s troops on horseback, but is confronted by Xian Lang, who knows that Mulan is hiding her gender. She attempts to kill Mulan, who is saved because of her leather armor that she used to hide her feminine figure. Mulan decides to stop hiding her gender, and rides back to battle, causing many Rourans to flee when they suspect she is a witch. The Rourans begin attacking with a trebuchet, but Mulan routs them and begins attacking from above. The Rourans turn their trebuchets towards Mulan, but their attacks trigger an avalanche, which buries them.
Mulan rides back to camp and rescues Chen Honghui, a fellow soldier who she befriended, but reveals that she is a woman. She is expelled from the army and begins her return home. On her way, she is confronted by Xian Lang, who reveals that she was an outcast for being a powerful woman, and the only way she can gain power is under Bori Khan’s leadership. Additionally, she reveals that the attacks on the outposts have been a diversion, as Bori Khan intends to capture the Emperor, who killed his father. Risking execution, Mulan returns to her battalion to tell them of the impending capture. Tung decides to believe her, and sends a unit to the Imperial City.
Xian Lang disguises herself as the Chancellor, and advises the Emperor to meet Bori Khan for single combat, while removing the city guard from their posts. Bori Khan kills the Emperor’s guards, and prepares to burn the Emperor alive in revenge. Mulan arrives in the city as the Rourans begin their attack, and races to free the Emperor. Bori Khan shoots an arrow at Mulan, but Xian Lang, who admires Mulan for leading her army openly as a woman, transforms into a bird and sacrifices herself by catching the arrow. Mulan fights with Bori Khan and kills him, but loses her father’s sword in the process. She frees the Emperor, who offers to let her join his personal guard. She declines the offer and returns to her village, where she is reunited with her family. An emissary from the Emperor, under the leadership of Commander Tung, arrives to present Mulan with a new sword, and offer her another chance to join the Emperor’s Guard.