The terrain is largely mountainous, especially in the north and west. A series of high mountain chains spreads across the province. There is a distinct canyon region to the west and a plateau region to the east. Yunnan's major rivers flow through the deep valleys between the mountains.

The average altitude is 1,980 meters. The mountains are highest in the north where they reach more than 5,000 meters; in the south they rise no higher than 3,000 meters. The highest point in the north is the Kawagebo Peak in Deqin county on the Diqing Plateau, which is about 6,740 meters high; and the lowest is in the Honghe River Valley in Hekou county, with an elevation of 76.4 meters.

The Nujiang River

The eastern half of the province is a limestone plateau with karst scenery and unnavigable rivers flowing through deep mountain gorges; the western half is characterized by mountain ranges and rivers running north and south. These include the Nujiang (Thai: Salween) and the Lancangjiang (Thai: Mekong). The rugged, vertical terrain produces a wide range of flora and fauna, and the province has been called a natural zoological and botanical garden.

Yunnan has a generally mild climate with pleasant and fair weather because of the province's location on south-facing mountain slopes, receiving the influence of both the Pacific and Indian oceans, and although the growing period is long, there is little arable land.

January average temperatures range from 8°C to 17°C; July averages vary from 21°C to 27°C. Average annual rainfall ranges from 600 mm to 2,300 mm, with over half the rain occurring between June and August. The plateau region has moderate temperatures. The western canyon region is hot and humid at the valley bottoms, but there are freezing winds at the mountaintops.