NOVELTY - A solution system of electro-deposited metal gallium and gallium alloy comprises (mol/L) metal salt (0.05-0.5), conductive salt (1.0-4.0), complexing agent (0.0-0.8), organic acid (0.5-3.0), organic additive (4-20), and water as solvent; where the pH value of the solution system is adjusted to 1-6 with saturated alkaline solution.    USE - The solution system of electro-deposited metal gallium and gallium alloy is useful for preparing copper, indium, gallium, selenide thin film soar cell (claimed).    ADVANTAGE - The solution system has good covering and dispersing property and long service life. Moreover, the prepared Ga thin film is bright, even and without fault; where the thickness and component of metal thin film can be changed optionally by controlling the deposit condition. Additionally, the preparation process is simple; the apparatus investment is low; and the cost is low.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are:    (1) a preparation method of the solution system of electro-deposited metal gallium (Ga) and Ga alloy comprising: (a) respectively dissolving metal salt, compelxing agent, and organic acid into water, and confecting into saturated solution for future use; (b) adding metal sat solution, organic acid solution, complexing agent solution, and organic additive into the water in turn and uniformly stirring; and (c) adjusting the pH value of the solution by alkaline solution; and    (2) an application method of the solution system of electro-deposited metal Ga and Ga alloy for preparing copper, indium, gallium, selenide (CIGS) thin film soar cell, comprising using electro-deposited copper (Cu)/sputtered molybdenum (Mo)/glass, metal foil, or plastic as cathode, using metal anode or titanium mesh as inert anode, arranging in the solution system, interconnecting a constant power supply or constant potential supply, and obtaining the Ga thin film; where the current density is 20-200 mA/cm2; and the solution temperature is 10-60 degrees C.