Ammonium metatungstate solution is an aqueous solution of AMT, ammonium metatungstate (NH₄)₆H₂W₁₂O₄₀.XH₂O is the isopolyacid-ammonium salt of tungsten, a tungsten compound with a large molecular weight and high water-solubility. AMT is extremely easily soluble in water, and as the temperature increases, its solubility in water increased, and ammonium metatungstate solution is the raw material of downstream products through liquid phase method.

Preparation of ammonium metatungstate solution can be divided into two categories of solid and liquid phase transformation. Typical solid phase transformation process is thermal decomposition method based on raw materials of APT, which by controlling the decomposition temperature and the partial pressure of ammonia and water to make most of the water-insoluble APT transferred into amorphous substance of water-soluble AMT, then dissolved in water to form ammonium metatungstate solution, and finally concentrated and crystallize to obtain the solid AMT. While the phase transformation is generally based on raw material of (NH₄)₂WO₄ solution, and obtain ammonium metatungstate solution through acid neutralization, extraction, ion exchange or ion-exchange membrane electrolysis method, and further concentrated to obtain crystalline AMT.