Beginning from the Yaoyue (Inviting-Moon) Gate and ending with Shizhang Pavilion, the Long Gallery ingeniously links Longevity Hill with Kunming Lake. Seven hundred twenty-eight meters (796.2 yards) in length, it is the longest gallery in Chinese gardens. In 1990 it was rated as the top long gallery of the world.

Two hundred seventy-three rooms with various paintings attract visitors into a fantastic land. Among them, they are studded with four octagonal pavilions on the joint between a higher place and a lower one, each symbolizing a season. Long Gallery was constructed along the natural terrain of Longevity Hill and the turns of Kunming Lake, offering a picturesque view with each step. In 1755 when Emperor Qianlong (1711-1799) built the gallery, he ordered artists to go to Hangzhou in Zhejiang Province to sketch the scenery there. Upon their return they painted 546 paintings of West Lake landscapes in the Long Gallery. The themes taken from historical figures, landscapes, flowers and birds can be seen as a miniature representation of the breadth of Chinese art. Appreciating the intricate paintings while listening to the profound stories, myths and legends, for example, Pilgrimage to the West, visitors can learn a lot about the five-thousand-year-old Chinese culture.

Worthy of mention is the fact that the main part of each picture followed the semicircular line of a girder; there was no set framework for the painting; images were created from artists' inspirations. Most of the paintings are typical "Sushi Colored Paintings" (a kind of Chinese classical painting, decoration art on a wooden building).