The paint film maintenance method of subway vehicle during the two million kilometres period needs to fit the market demand of efficient,environment friendly and low-cost.The aging paint film state on the vehicle surface was analyzed in this paper,and the maintenance method of water-based paint on the aging paint film was discussed.The checkpoints of appearance,adhesion,gloss,aberration in paint film maintenance area were validated which could meet the standard requirement.This maintenance method can get high-quality painting effect.