Hongyi Pavilion is located on the west side of the square in front of the Hall of Supreme Harmony, facing east, opposite to Tijen Pavilion. Founded in the 18th year of Yongle in the Ming Dynasty (1420), it was called Wu Lou in the early Ming Dynasty, Wu Chengge in Jiajing and Hongyi Pavilion in the early Qing Dynasty. In the Qing dynasty, it was the treasury of the Ministry of Internal Affairs, keeping gold and silver, coins, jewelry, jade articles, gold and silver utensils and so on. The gold and silver utensils used by emperors and queens for banquets are all prepared by the state treasury, and they are still kept by the state treasury after use. As a foil to the Hall of Supreme Harmony, Hongyi Pavilion and Tijen Pavilion are symmetrical, and the architectural forms are exactly the same. Tijen Pavilion was destroyed by fire in Qianlong period and rebuilt in Hongyi Pavilion. There are nine 25-meter-high heavy buildings. Because the second pavilion is the hatchback of the Hall of Supreme Harmony, the shapes cannot be too different, which will affect harmony. Therefore, it is built in the form of a pavilion, with a waist eaves and a seat between the two floors, and a single eaves on the roof. This makes its height reach 23.8 meters, equivalent to 7/ 10 of the height of the Hall of Supreme Harmony, which is higher than the adjacent one. The coordination between the second pavilion and the main building makes the whole complex more magnificent.