NOVELTY - A methylamino bismuth iodide thin film preparing method involves mixing methylamine and hydroiodic acid at low temperature, warming and evaporating to obtain powder, dissolving powder in ethanol, heating, cooling, precipitating methylamine iodine to obtain purified methylamine iodine. The methylamine iodine powder is dissolved in solvent, stirring to concentration of 0.3-1.5mol/l methylamine iodine solution. The solution is coated to substrate of fluorine-doped tin oxide transparent electric conduction glass, indium tin oxide on transparent conductive glass or silicon wafer.    USE - Method for preparing methylamino bismuth iodide thin film for photovoltaic solar cells.    ADVANTAGE - The method enables preparing methylamino bismuth iodide thin film with high photoelectric conversion characteristics, in simple, easy, environmentally friendly and cost effective manner.    DETAILED DESCRIPTION - A methylamino bismuth iodide thin film preparing method involves mixing methylamine and hydroiodic acid at ratio of 1: 1-1.5 at low temperature of -10 to 10 degrees C for 1- 2 hours, warming at 50-70 degrees C and evaporating to obtain powder, dissolving powder in ethanol, heating the mixture at 30-80 degrees C, cooling at -30 to 0 degrees C, precipitating methylamine iodine, repeating twice to obtain purified methylamine iodine, and heating at 50-70 degrees C, and drying to give methylamine iodine powder collecting stand. The methylamine iodine powder is dissolved in an organic solvent such as dimethylformamide or gamma-butyrolactone, stirring at room temperature, to a concentration of 0.3-1.5mol/l methylamine iodine solution, and placed in a beaker. The bismuth solution and methylamine iodine solution are mixed at a molar ratio of 1.5-3:1, heated and stirred. The solution is dropwise coated on to the substrate of fluorine-doped tin oxide transparent electric conduction glass, indium tin oxide on a transparent conductive glass or silicon wafer by using a spin coater at speed of 2000-4000 rpm for 10-20 seconds to obtain finished product.