The "red fight" between Moon and Flying-Snow was filmed in a forest in Mongolia. Director Yimou Zhang had to wait until the leaves turn yellow, and hired local nomads to gather even more yellow leaves in order to cover the ground completely. In fact, he was so fanatic about the leaves, that he had his crew separate the leaves into four different "classes" which were each put at increasingly farther lengths from the camera.
The emperor remarks, after hearing Nameless tell him that there are 19 ways to write the word "sword", that he would solve this problem. In history, he succeeded in enforcing only one writing system in the whole of China. This way, whatever dialect people speak, they would be using the same set of characters making communication a lot easier.
In ancient China, when someone claimed that he killed his enemies, he needed to present their heads (tou zi) as proof instead of their weapons. Director Yimou Zhang modified this, mindful of the audience's stomachs, thus making the story less accurate.
All of the soldiers in the Qin army sequence as well as the palace sequences were performed by actual Chinese People's Liberation Army soldiers, except the stunt performers. It's estimated that 18000 were used as extras in the film.
The lake scenes took almost three weeks to film because director Yimou Zhang insisted that the lake's surface had to be perfectly still and mirror-like during filming. Due to the natural currents, this occurred every day for only two hours starting at 10am. To adjust to this phenomenon, the filmmakers arose at 5am each day to begin five hours of preparation and set-up.
Director Yimou Zhang did not like the initial batch of the red cloth used in the "red sequence"; none of the test samples came out right on camera. Therefore, a special shade of red dye was Fedex'ed from England, and costume designer Emi Wada ended up dying the cloth AND making all the costumes locally (with help, of course).
The Qin Empire preferred the color black, even for the horses. In order to be historically accurate, Director Yimou Zhang ordered all 300+ horses to be colored black (temporarily, of course) for the cavalry sequences.
Maggie Cheung required weeks of training. Even Ziyi Zhang, who earned rave reviews with her martial arts performance in Crouching Tiger, Hidden Dragon (2000) needed intensive training to become adept with the twin blades she fights with during many of her scenes in Hero.
Originally released in 2002 in Asia, it would not be another two years until this film was released in the United States. Studio executives were concerned that the foreign-language film would not be successful at the box office with American audiences. When the film debuted in August 2004, it surprised many by opening at #1 with $18 million in receipts. It would go on to gross $53 million, becoming the 3rd highest grossing foreign film to date in the United States.
Robin Shou was the original choice for the role of Sky but dropped out for unknown reasons. Jet Li then suggested to the director that Donnie Yen would make the perfect opponent for Jet's own character.
Miramax originally acquired the U.S. distribution rights in 2002 after the film's huge success in Asia. However, the film did not receive its U.S. theatrical release until 2004. Before the release of the official U.S. version, the film gained a cult following in the States via "official" copies of the DVD from other countries.
Rongguang Yu was originally considered for choreographing the film's action scenes. It was also through Jet Li that Yu got the opportunity but Yu felt his style of choreography was too traditional so he turned down the offer. The job was handed to Wei Tung instead followed by Siu-Tung Ching.