The invention discloses a method for preparing an active metal based alloy, which belongs to the field of non-ferrous metallurgy and comprises the following steps: adopting a molten salt electrolytic codeposition method; selecting an alloy using a relatively active metal as a matrix; using chloride and oxide of alloying elements as raw materials; electrolyzing the raw materials in an alkali metalmolten salt system; and controlling the electrolysis temperature to be between 400 and 1,200 DEG C to melt the materials. A mode of adding the raw materials continuously is adopted so that the proportion of each alloying element of the added raw materials accords with that of the designed alloy components, and the faraday electric quantity of the added raw materials in corresponding time intervalaccords with the electrolysis electric quantity simultaneously. The alloy obtained through electrolyzing can be taken out at any time and is consistent with the design components. The process is simple, convenient and practicable, and is suitable for the development of continuous production.