Following a remark by his Majesty the King, the Forestry Department of Thailand directed officers to make a survey in the forests, where the Petchaburi and Pranburi rivers originate, to acquire data about the forest conditions. The result was that this area features beautiful sceneries, waterfalls, caves, lakes and many high economic valuable woods. Besides it is home to a diversity of wildlife, such as mountain goats, gaurs, barking deer, monkeys, langurs, gibbons, bears, tigers, leopards and elephants. Therefore, it was decided that the area highly deserved the title of a national park to be kept and preserved as a national treasure. Finally, on 20th April 1983, the Forestry Department of Thailand officially announced the area as a national park.

The Tenasserim Range, running along the Thai-Burmese border cuts through the park with its highest peak rising to 1207 metres. The park's abundant streams and rivers have been used to flood the 45 square kilometres Kaeng Krachan Reservoir, that is supplying farmers in the coastal lowlands with the necessary water and has become an easy to reach tourist attraction.

The national park area consists mainly of broad-leaved evergreen forests covering a complexly arrangement of mountains at an average height of 500 meters above the sea level. The geology is mainly granite with some limestone mountains rich in fluorite ore. The average rainfall is more than 1000 millimetres a year, with 90 percent falling from June to September.

Today, Kaeng Krachan National Park, is the largest national park in Thailand, covering 2,915 square kilometres in Petchaburi and Prachuab Kiri Khan provinces. It is the most delicious dish for forest trekkers and mountaineers, offering rambling routes through rich forests and spectacular activities like bird and butterfly watching. Regular spotted animals include Malayan pangolin, Malayan porcupine, wild pig, sambar deer, barking and lesser mouse deer, clouded leopard, elephants, Asiatic black bear and more than 250 bird species.

One main road starts from the park entrance and along this is a network of trails has been established. Tor Tip Waterfall is a major tourist attraction and can be reached by 4WD truck. This huge 18-tier waterfall is beautifully painted with lovely streams. Another tourist attraction is Phanern Thung Mountain that offers a spectacular view across the valleys.