It is located on the west side of the south gate of Beihai. In the Yuan Dynasty, it was a small island. When it was rebuilt in the Ming Dynasty, the city wall was built and two water surfaces in the southeast were leveled, which basically formed the present scale and surrounding environment. In the 19th year of Qing Emperor Kangxi (168), Chengguang Hall was rebuilt, and the original semi-circular hall was changed into a cross-shaped plane. During the Qianlong period, a large-scale construction was carried out and a jade urn pavilion was added. Today's Tuancheng is basically a building complex built during the Qianlong period. Its plane is circular, and it is surrounded by a small town with thousands of bricks. The city platform is 4.6 meters above the horizon, with a circumference of 276 meters and an area of 4,553 square meters. There is a wall-following door under the east and west side walls, and a gatehouse is built on it, with Zhao Jing in the east and Yan Xiang in the west. The entrance can be climbed to the top of the city along the footpath. Cover doors are set at the footpath, and the layout of buildings on the platform adopts the layout method of symmetry and garden. Chengguang Hall is the center of the whole city platform, with Jade urn Pavilion in the south and Jingji Hall in the north, which forms the central axis of the city platform. Symmetrically arranged on both sides, there are Gulaitang, Yuqingzhai Dongdao and Xidao. Duoyun Pavilion and Jinglan Pavilion stand high on the rockery. The whole city platform has yellow tiles and red walls. Among the magnificent ancient buildings, dozens of pines and cypresses have been planted all over. The center of Chengguang Hall is square, with three rooms in width and three in depth, and one in Baoxia on all sides. The whole plane is cross-shaped. There is a platform in the south. In the middle of the hall, there is a double-eaves resting on the top of the mountain, and the Baoxia is a single-eaves resting on the top of the mountain, covered with yellow glazed tiles and green trimmed tiles, and the cornices are upturned. The upper eaves are heavy with seven arches, while the lower eaves and the Bao Xia are heavy with five arches. In the hall, a large gold spiral painting is put on. The jade urn in the jade urn pavilion is a work of the Yuan Dynasty, with large volume and exquisite carving.

after the founding of the People's Republic of China, the government attached great importance to the protection of Beihai and Tuancheng. In the early 195s, the bottom of the lake was dredged, 116, cubic meters of silt was removed, and nearly 1, cubic meters of garbage in the park was removed, and the revetment was protected and the road surface was paved.

In 1954, due to the widening of the Jade Bridge in Jin Ao, the southern part of Tuancheng was demolished. Zhou Enlai personally visited Tuancheng and finally decided to keep it. He also instructed to build a step in the north of Tuancheng to connect Tuancheng with Beihai, but don't tear down the wall and dig holes. Since 1953, the state has allocated nearly 2 million yuan to basically repair all ancient buildings, install lightning rods on tall buildings, and modify circuits and pipelines to avoid fires. At the same time, sewage pipes were built to intercept 36 sewage sources flowing into the lake. Since 1984, close-range photography and mapping of the ancient buildings in the whole park have been carried out, and the archives have been gradually established. At present, there are specialized agencies responsible for protection and management.