Inorganic perovskite semiconductor Cs2SnI6 is a promising solar light absorber material to replace its unstable organic-inorganic counterpart in perovskite solar cells. However, at present its synthesis method is still complex and expensive. Here we report a simple one-step solution method to synthesize the Cs2SnI6 powder, and then the effects of reactant type, reactant ratio and reaction solvent on the purity, crystallinity, optical and electrical properties, air and thermal stability of the Cs2SnI6 power were studied. We find that pure and crystalline Cs2SnI6 powder can be achieved in acetonitrile or anhydrous ethanol with a CsI:SnI2 ratio of 1:1, or with a CsI:SnI4 ratio of 3:2 (or 2:1). Cs2SnI6 film with better crystallinity usually has a stronger optical absorption, a lower carrier concentration, a higher carrier mobility, and a better air and thermal stablity. Optical absorption of Cs2SnI6 synthesized in anhydrous ethanol and acetonitrile keeps almost unchanged at the anneal temperature up to 150 degrees C.