Khanom district is in the north of the province. To the west is Surat Thani Province, while to the north and east is the Gulf of Thailand. Neighboring districts are (from the south clockwise) Sichon of Nakhon Si Thammarat and Don Sak of Surat Thani.
Khanom has been described as a hidden paradise with pink dolphins, the latter not that uncommon around its shores. Most of the coast line of district will be protected as part of the Hat Khanom - Mu Ko Thale Tai National Park, which is in the process of creation. The coast of the district consists of a series of beaches among the limestone and shale mountains of northern Nakhon Si Thammarat Range. Nai Plao Beach is the most popular of these beaches. Several caves are found in the hills, the most famous one is Khao Wang Thong cave.