Microwave absorbers with unique optical and mechanical performance are urgent for complex electromagnetic environment. Here, we demonstrate the mechanically flexible, optically transparent, and microwave-absorbing polyacrylamide (PAM) hydrogel, in which the polar water molecules with high polarization contribute to the efficient microwave attenuation, but the binding between water molecules and PAM will slow down the orientation polarization of polar molecules. Meanwhile, the dominated dielectric property of water molecules in PAM hydrogel determines that the molecules displacement in polymer mixture is feasible for manipulating permittivity. Besides, by decreasing temperature, the flexible and transparent hydrogel will switch to rigid and opaque state as the phase conversion between amorphous and polycrystal state. By constructing structures with such hydrogel, the obtained absorber also exhibits the optical and mechanical switchable properties, covering the effective absorption within 5.7–18 GHz. This work provides an effective method to fabricate optically and mechanically manipulable microwave absorbers for intelligent electromagnetic stealth systems.