According to legend, at some time in the Satya Yuga, Daksha performed a yagna (named Vrihaspati) with a desire of taking revenge on Lord Shiva. Daksha was angry because his daughter Sati had married the 'yogi' God Shiva against his wishes. Daksha invited all the deities to the yagna except for Shiva and Sati. The fact that she was not invited did not deter Sati from attending the yagna. She had expressed her desire to attend to Shiva who had tried his best to dissuade her from going. Shiva eventually allowed her to go escorted by his ganas (followers).
But Sati, being an uninvited guest, was not given any respect. Furthermore, Daksha insulted Shiva. Sati was unable to bear her father's insults toward her husband, so she committed suicide by jumping into the yajna fire.
Enraged at the insult and the injury, Shiva destroyed Daksha's sacrifice, cut off Daksha's head, and replaced it with that of a goat as he restored him to life. Still crazed with grief, he picked up the remains of Sati's body, and danced the dance of destruction through the Universe. The other gods intervened to stop this dance, and the Vishnu's disk, or Sudarshana Chakra, cut through the corpse of Sati. The various parts of the body fell at several spots all through the Indian subcontinent and formed sites which are known as Shakti Peethas today.
In Purnagiri the Naabhi (Naval) part of Sati fell and people come here to worship the devi here.
As per a common belief, every person who comes here with sincere faith and devotion has his prayers answered. During Navratras, in the Chaitra month of the Indian calendar, devotees in large number come here to have their wishes fulfilled. After worshipping Mata Purnagiri, people also pay their tributes to her loyal devotee Bada Sidth Nath at Brahmadev and Mahendra Nagar in Nepal.