Abstract: The short-oil length waterborne alkyd resin was prepared through melting esterifaction and salified method.The influence of alcohol surplus r,acid value in polymerization stage and final acid value,molecular weight and distribution,the amount of trimellitic anhydride(TMA) on the water dispersibility of resin and coating properties were studied.The experimental results showed that resin with best performances could be obtained when r = 25%,acid value in polymerization stage was 20mgKOH/g,final acid value was 55~65mgKOH/g,and the amount of TMA was 1/4~1/5 of the molar of dicarboxylic acid.Molecular weight and distribution had great influence on the properties of resin.Normally the appropriate number average molecular weight was around 2500,and distribution coefficient was around 12.