Since the areas of Nam-wa Forest and Mae Charim Forest, the southeastern part of Nam-Nan Forest, and Huai Sali Forest situated in Tambon Nam-pang, Tambon Nam-pai of Mae Charim District, and Tambon Lai-nan, Tambon Sanna Nhong-mai, Tambon Nam-muab of Viangsa District, Nan Province, consist of valuable natural resources including plants, wild fruits and wild animals, as well as beautiful scenery of forests, mountains, streams, and cliffs, it is deemed expedient to establish Mae Charim Forest as a national park under the National Park Act 1961 for the purpose of conservation within an approximate area of 432 square kilometers or 370,000 rai.

Topography
The geographical features of the National Park consist of high mountains, extending from the north to the southwest, and Luang Phra-bang Mountains extending from the north to the south (and being used as the boundary between Thailand and Laos). The height of mountains lowers to the west. Doi Khun-lan, situated in the east of the National Park, is the highest mountaintop (1,652 meters above the medium sea level) where Wa River flows from Luang Phra-bang Mountains passing the west of the area for approximately 7.5 kilometers.

Climate
The weather at the National Park can be divided into 3 seasons, including summer (March-May), when the area of the National Park is affected by the summer monsoon blowing from the southeast of Andaman Sea; the rainy season (June-October), when the area of the National Park is affected by the southwestern monsoon; and winter (November-February), when the area of the National Park is affected by the northeastern monsoon blowing the coldness from the North Pole to Thailand.

The average annual rainfall of 1,206.29 mm can be measured at the Meteorological Office of Nan Province during 1992-1998. The average maximum rainfall of 319.9 mm can be measured in August; and the average minimum rainfall of 6.19 mm can be measured in January.

The average temperature of 26.8„aC can be measured during 1995-1998. The average highest temperature of 30.0„aC can be measured in May; and the average lowest temperature of 22.2„aC can be measured in January.

The average relative humidity of 76.43 percent can be measured during 1995-1998. The average highest relative humidity of 84.6 percent can be measured in August; the average lowest relative humidity of 63.04 percent can be measured in March; and the average annual relative humidity is 76.9 percent.