High magnetic loss and saturated magnetic conductivity endow FeSiAl sheets with broadband microwave absorption properties. However, due to thick sheet thickness and rigid sheet, the mechanical properties and flexibility of FeSiAl films are poor, greatly influencing its use in flexible electronic devices. In this study, a small amount of water was introduced into the aramid nanofiber (ANF) suspension to recover their intermolecular hydrogen bonds. By controlling the water content, the FeSiAl/ANF nanocomposite films exhibit excellent mechanical properties and flexibility. The results indicate the nanocomposite films show high flexibility and good microwave absorption properties when the ANF mass fraction reaches 60%. The stress and strain of the nanocomposite films can reach 136.88 MPa and 4.72 %, respectively, by using universal mechanical tester. When the thickness reaches 3 mm, the effective absorption bandwidth and reflection loss are 2.84 GHz and -46.81 dB tested by vector network analyzer and simulation. Besides, the nanocomposite films can resist folding circles. The easy and green preparation process endows the nanocomposite films with great potential application in the microwave absorption field of flexible electric devices.