This article described the development and application process of metallic basecoat for urban rail vehicle and EMU. Compare to solid color topcoat，the painting process is more complicated for metallic basecoat. A typical urban EMU train is 18~23 m in length and 3 m in height，with large areas to be coated. It was very hard to control the defects of flooding and color difference during the spray process. In this article，factors which related to the property of the metallic basecoat such as key raw material like hydroxyl acrylic resin and butyl acetate cellulose，formulation method were studied. The final metallic basecoat product showed excellent stability in color difference and visual appearance，high weatherability and could be sprayed easily in large surface area such as carbody of urban rail vehicles and EMU.Nowadays，the product has been widely used in several urban rail lines and EMU trains indifferent cities like Guangzhou，Shenzhen and Urumqi.