In order to simplify the process of biodiesel preparation through transesterification and make the technique more environmental friendly, using Ba(OH)2 as the catalyst was studied in present work. The experiments were conducted using L9(34) orthogonal test, three kinds of factors which were the molar ratio of oil to methanol, amount of Ba(OH)2 and the reaction temperature were investigated. By statistical analysis, the optimal conditions for the reaction were obtained, that a 1:6 molar ratio of oil to methanol, 2.0% Ba(OH)2 catalyst and 60℃ reaction temperature, under these conditions a 94.27% conversion rate for soybean oil methyl ester was gained at 90min, and the conversion rate exceeded 95% while linseed oil, peanut oil and rapeseed oil were taken as the raw materials. In addition, the transesterification results catalyzed respectively by Ba(OH)2 and KOH were compared, the experimental results showed that the activity of Ba(OH)2 was as high as KOH, the main components of fatty acid methyl esters in the two kinds of biodiesel were identical, and Ba(OH)2 could be removed easily and completely by deposition and centrifugation. So Ba(OH)2 could be a promising candidate catalyst for biodiesel preparation.