The high elasticity waterborne epoxy primer for locomotive and rolling stock Was prepared by serf-made CTBN modified epoxy emulsion and medium molecular weight epoxy emulsion as film-forming material,collocation of ultra_fine mica powder,diatomite and waterborne aliphatic amine curing agent.The main factors affecting the performance of the coating were studied.The results showed that the hiigh elastic waterborne epoxy primer had good high and low temperature cycling performance,salt spray resistance and chemical resistance.