This work focused on the preparation of microwave-absorbing adhesive film, which was a crucial material in the structure–function integrated wave-absorbing components. The adhesive film containing iron powder was prepared using the calendaring method and the regulation of the absorption frequency was realized by introducing trace amounts of carbon nanotubes. The structure and properties of the adhesive film were further characterized using scanning electron microscopy (SEM), dynamic thermo-mechanical analyzer (DMA), and vector network analyzer (VNA). The results indicated that the absorption frequency band of the iron-containing film was mainly concentrated in the high frequency range, covering the 10–13.25 GHz band. The absorption peak frequency of the film was significantly shifted from 11.45 to 4.68 GHz in the lower frequency range with the trace addition of 0.5 wt.% carbon nanotubes. The regulation mechanism of carbon nanotubes on the absorption frequency of the film was further discussed based on the electromagnetic parameter measurements, combined with the analysis in the loss mechanism and impedance matching of the two films.