The invention discloses a novel acidic molybdenum aluminum molybdenum etching liquid and its preparation process. The novel acidic molybdenum aluminum molybdenum etching liquid comprises phosphoric acid, acetic acid, nitric acid, metal nitrate, a cationic surfactant and pure water. The preparation process of the etching liquid includes: maintaining the rotation speed of an ingredient tank stirrer, adding the phosphoric acid, the acetic acid, the nitric acid, potassium nitrate, the pure water and the cationic surfactant sequentially into the ingredient tank, fully stirring them, then introducing the mixture into a filter to conduct filtration, thus obtaining the molybdenum aluminum molybdenum etching liquid. The molybdenum aluminum molybdenum etching liquid provided in the invention has a small particle size and high purity, has a basically consistent etching rate on different metals, and is stable in reaction. By adjusting the nitric acid concentration, the etching speed can be controllable. The substrate etched by the etching liquid has a clean and tidy surface, no residue, and no intermetallic layering phenomenon. The remaining lines are smooth, and the etching angle is maintained at 40-60 degrees.