Amorphous CoMnNiO film is doposited on oxidized Si substrate by RF sputtering equipment. Structure relaxation occurs in the amorphous CoMnNiO film when it is annealed below 550°C. Annealed in the range from 600°C to 1000°C, the amorphous film is converted into the polycrystal. After annealing in rich oxygen atmosphere, the amorphous film is transformed into spinel solid solution with stable structure and good electrical properties. The electrical conductivity will be reduced due to formation of low valence oxides when annealed without oxygen. As annealing temperature is higher than 1000°C, some spinel solid solutions will be resolved into low valence oxides CoO and NiO, reducing the conductivity of the CoMnNiO film.