The invention discloses a method for pretreating automobile coating. The method comprises three steps of high-pressure water pre-cleaning, degreasing and secondary washing, wherein water in a washing tank for secondary washing flows through a water pump to be fed into a high-pressure washing tank, the high-pressure washing tank is connected with a high-pressure spray gun for high-pressure water pre-cleaning through a pipeline, so that the water after the secondary washing can be used for high-pressure water pre-cleaning. In addition, the bottom of a degreasing tank is connected with the water pump through a pipeline , a flow control valve is arranged on the pipeline so that degreasing fluid in the degreasing tank can be used for high-pressure water pre-cleaning. According to the method for pretreating automobile coating, clean water and a degreasing agent can be repeatedly utilized, a small amount of waste water is discharged, water is saved, and a good pretreating effect is obtained.