Abstract: Based on the electrostatic self-assembly principle, self-assembly film were prepared by using poly diallyl dimethyl ammonium chloride (PDDA) and poly (sodium 4-styrenesulfonate) (PSS).In the experiment, the absorbance changes of the film in the assembly process was investigated.Through the method of adding the Fe³⁺ indicator that was sulfosalicylic acid in PDDA and PSS self-assembly system, self-assembly film with iron ion sensitivity were prepared.The morphology under scanning probe microscope showed that the sensitive film prepared was integrated and uniform.The optical performance test indicated that the sensitive film in solution of different concentration of iron ions had a good corresponding relationship with absorbance change of the sensitive film and iron ion concentration.