The invention belongs to the field of environment production water treatment. A phosphorus-free cleaning prefilming agent mainly comprises two components that are independently packaged, wherein component A is a phosphorus-free complexing agent, the component B is a phosphorus-free pickling agent, and the weight part ratio of the component A to the component B is (10-30):(4-7). The agent mainly comprises sodium gluconate and boric acid, wherein sodium gluconate is classic organic acid and has certain iron ion chelation and corrosion inhibition effects; and the cleaning prefilming agent is phosphorus-free and biodegradable, has excellent corrosion inhibition and scale inhibition effects, and can meet sewage discharge standard. Boric acid is commonly used inorganic acid in industrial and civil applications, and no discharge concentration of boron is found in the current wastewater discharge standard. Boric acid can be used as rust inhibitor, lubricant and thermal oxidization stabilizer and the wastewater discharge standard can also be met. The two components are reasonably compounded and applied to ensure good cleaning and prefilming effect, without generating corrosion.