The park is situated on the Andaman sea coast in Satun and Trang provinces. It consists of an area of coastline and over 30 islands. The park has many diverse habitats including; open water, coral fringed islands, sandy beaches, forest covered islands to sheer rocky islands which rise steeply out of the sea. There are also a few patches of mangrove forest, beach forest and tropical forest. The islands within the park are small the largest being Khao Yai Island which is about 4.7 sq.km in area. The sea area of the park includes many important fishing grounds for this reason many of the islands act as temporary refuges for fishing boats during monsoon storms.

The park was established by royal decree on the 31st December 1984. The park covers a total area of 494.38 km2, of which 468.38 sq.km or 94.74% is open water. Mu Ko Phetra is the third protected area in Satun province and is the 14th Marine park in Thailand.

The topography of the park is dominated by Limestone rocks which were deposited in a shallow sea around 470 million years ago, during the Ordovician period. This rock unit was laid down over a very long period of time and as a result in places it is over 2,750m thick. Limestone rock is impermeable but is soluble in water. Thus over a long period of time water seepage through natural fissures results in the fissures enlarging to form a variety of structures and eventually caves. This process results in some fantastic landforms being observed at Phetra National Park.

Mu Ko Phetra National Park is located in the Tropic Zone with rather constant temperature and rainfall all year round. The rainy season, therefore, may seem quite lengthy but the months with most heavy rainfall are May through October. From the end of November until March, the rainfall will start to decrease, shifting into a short period of Summer from March to April which is also the period of transition for the Monsoon season (from Northeast Monsoon to Southwest Monsoon). As for the transition from the Southwest Monsoon to the Northeast Monsoon in October, although such transition can cause some variation in climate, no major differences can be detected.

Types of vegetation on the Mu Ko Phetra National Park can be divided into 4 categories
Rain Forest scatters around the islands. Common vegetations found are Hopea ferrea , Ironwood and Kradon. Grounds covering plants found are fern, rattan, moss and ginger/galangal species

Open Forest found along the beach and common vegetations are Casuarina equisetifolia , Calophyllum inophyllum, Hibiscus tiliaceus , Thespesia populneoides, Terminolia catappa, Dialium cochinchinense and Barringtonia asiatica. Grounds covering plants found are Pandanus odoratissimus.

Mangrove Forest found in the muddy area by the sea and mouth of the canal. Common vegetations are Rhizophora mucronata (Red Mangroves) , Rhizophora apiculata, Brownlowia peltata , Xylocarpus moluccensis , Xylocarpus granatum, Bruguiera parciflora and Bruguiera cylindrica.

Aquatic life such as seaweeds and planktons can also be found.

Wildlife
Prominent birds found are Haliacetus leucogaster, Haliastur indus (Brahminy kite) and Spilornis cheela (Crested).

Common mammals in the area are Nycticebus coucang, Presbytis Cristata (Silvered langur), Trangulus javanicus, Sus Scrofa (wild pig) and bats.

Reptiles found are Python reticulatus (Regal Python) and Varanus nebulosus (Indian Monitor) and etc.

Marine Life, The waters around the park are clear and thus support an abundant marine fauna. Most of the islands have coral reefs those found around the outer islands being especially diverse. Coral types commonly seen include Brain coral, Staghorn coral, Soft coral, Plate coral and Mushroom coral. The sea is also rich in economic marine species, and many fish, crabs, lobster and squid are caught from the waters surrounding the park.