Kaeng Krachan is located on the eastern slope of the Tenasserim Mountain Range at the border of Burma (Myanmar). It occupies the western half of Phetchaburi Province (Amphur Kaeng Krachan and Amphur Nong Ya Plong) and a portion of northern Prachuab Khiri Khan Province (Amphur Hua Hin).
The National Park was designated on June 12, 1981; its original borders encompassed 1.5 million rai. On April 20, 1983, Thalerng Thamrongnawasawad, Peramnent Secretary of the Ministry of Agriculture and Cooperatives, presided over the offical opening ceremony. On December 27, 1984, the park area was extended, as proposed by the Hua Hin Environmental Conservation Group, to cover the boundary between Phetchaburi and Prachuab Khirikhan Provinces, bringing the total area to over 1.8 million rai.
         The area, about 45 squares kilometers, consists of both ground and water in reservoir. The vastly forest upper the Kang Kra Jan Dam is on complicated mountain ranges which the highest peak is 1,200 meters above sea level and approximately high 500 meter above sea level. Most of the mountains are Granite Mountain, few are Limestone Mountains, and many are full of fluoride. And also most of the area is covered by rain forest so that is the source of Phet Buri River and Pran Buri River.
          The park is compossed of two major watersheds. About half of the area drains to the Phetchaburi River, which flows to Kaeng Krachan dam at the eastern edge of the park and then down through farmland to the provincial capital of Phetchaburi. The southern haft of the park drains to the Pranburi River, which flows south to the Pranburi dam and then on to the town of Pranburi in Prachuab Khiri Khan Province. Because of abundant rainfall and undisturbed forest cover in these watersheds, the streams, waterfall and rivers of Keang Krachan flow year round. The park is composed of two major watersheds and a large evergreen forest. About half of the area drains to Phetchaburi River, which flows to Kaeng Krachan dam and the southern half of the park drains to the Pranburi River. Humidity remains high throughout the year, with heavy rain during the rainy season and cool weather for much of the year. The steep forested areas of the park are even more humid than the young forest and cleared lands in the lower elevations.