The invention provides weather-resistant steel rust layer stabilizing treatment fluid. Each liter of water contains 54-90 g of phosphoric acid, 15-30 g of zinc dihydrogen phosphate, 3-8 g of nitrate, 3-8 g of manganese sulfate, 3-6 g of molybdate and 1-3 g of a surfactant. A film layer formed on the surface of weather-resistant steel belongs to chemical conversion films, is a non-metal film, is low in electroconductivity, and capable of effectively inhibiting electrochemical corrosion and reducing corrosion speed. The formed film layer is a porous film and does not completely stop corrosion, a corrosive medium can enter along pores and react with a matrix, the corrosion speed is effectively controlled by the film layer, which is beneficial for forming the stabilized rust layer on the surface of the weather-resistant steel, and rust fluid sagging is prevented. Rust layer stabilization of the treated weather-resistant steel can be achieved after the weather-resistant steel is put outdoors for about half a year, and the phenomenon of rust fluid sagging is avoided. The steps are simple, operation is convenient, and practicability is high.