The invention discloses an acidic degreaser for preventing rack from being electroplated with copper. Each liter of the acidic degreaser comprises the following components, according to a ratio: 5-10 g of an inorganic acid, 0.05-5 g of a surfactant, 1-10 g of inorganic salt, and 1-5 g of a tin-dissolution resisting agent, with the balance being deionized water. The tin-dissolution resisting agent is pyrazole or a pyrazole compound. The invention further discloses a preparation method and an application method of the acidic degreaser. The acidic degreaser can prevent contact points of an electroplated rack from being plated with copper and tin during repeated electroplating. Problems that when a conventional acidic degreaser is used, tin dissolved by the acidic degreaser flows onto a board surface because of an action of gravity, thereby forming a conductive layer on a plating resisting layer, and copper and tin cover the plating resisting layer through electroplating in a subsequent electroplating process, resulting in difficult moulding of a circuit are overcome. Removal of copper and tin from the rack through washing after every time electroplating is avoided. Process steps are simplified, the production efficiency is increased, and the production cost is reduced.