The invention provides a method for quickly roughening concrete by retarder flushing. The method is characterized by comprising the following steps of: diluting retarder with water to form a retarder solution; uniformly spraying on the concrete surface of a bridge floor with an agricultural sprayer, so that the retarder and the concrete surface are sufficiently bonded; after the concrete is subject to initial setting, the concrete on the bridge floor is flushed at a certain dip angle by using a high pressure water gun, cement mortar on the surface is flushed by using the high pressure water gun; a broom is cooperated when the concrete surface is flushed, and floating slurry flushed by the water gun is swept by the broom, and uniform aggregate is exposed on the concrete surface; geotextile is used for covering after flushing, and watering is carried out for curing; and the bridge floor is cleaned with a powerful cleaning tanker before an asphalt waterproof layer is constructed, and the bridge floor is cleaned by blowing and sweeping.