In tungsten diiodide, the tungsten element has a valence of +2, and the iodine element has a valence of -1. Therefore, the quantity ratio of iodine to tungsten in tungsten diiodide is 2:1, which is determined according to the principle of electroneutrality.

There can be two methods of preparing tungsten diiodide using tungsten hexacarbonyl, the main difference between the two being in the choice of temperature.

Tungsten hexachloride (WCl₆), as one of the reactants, can be reacted with hydrogen iodide (HI) to prepare tungsten diiodide, but attention should be paid to the temperature of the reaction to reduce the chances of the formation of other products.

The high-temperature chemical method of tungsten diiodide is legally produced by the reaction of elemental tungsten and elemental iodine at temperatures between 600 and 800°C: W+I₂→WI₂. Generally, the temperature selected for the reaction is 800°C, and tungsten diiodide is produced using the reaction of tungsten powder with iodine.