The by-products of citrus fruits processing can be up to 50% of the fruit, which containing a lot of sugar that could be used to prepare molasses and be further fermented into alcohol. The conditions of producing malasses and alcohol were optimized. The amount of quicklime to extract syrup for preparing molasses from citrus processed residues was 0.3%. Molasses with 40% total soluble solid (TSS) was prepared in this study that contained 34% total sugar. The main factors affecting fermentation of the molasses including pH, sugar level, inoculums size of yeast and temperature were studied by means of single factor test, and then an orthogonal test was conducted to optimize the conditions. Optimal fermentation conditions to produce ethanol from molasses were as follows, initial pH 5.0, initial sugar level 25%, inoculums size 3×107/mL, fermentation temperature 30℃ and standing fermentation. Under the optimal fermentation conditions, a level 10.6% of alcohol was obtained. The results indicated that it's feasible to produce fuel alcohol by using molasses extracting from citrus residues.