Wearable mechanical sensors are susceptible to moisture, causing inaccuracy for monitoring human health and body motions. Although the superhydrophobic barrier on the sensor surface has been extensively explored as a passive water repel strategy, the dense superhydrophobic surface often has limited flexibility and inevitably degradates in high humidity or saturated water vapor environments due to the nucleation and growth of small size water molecules. This work reports a superhydrophobic MXene-sodium alginate sponge (SMSS) pressure sensor with efficient low-voltage Joule heating to provide sustained superhydrophobicity for moisture-resistant sensing. The superhydrophobic surface on the outside can repel large size water droplets, whereas the Joule heating efficiently removes small size water droplets and significantly reduces water molecule adsorption throughout the sponge. Because of the sustained superhydrophobic barrier and high porosity in the sponge, the SMSS pressure sensor with high sensitivity, large sensing range, and quick response can accurately and reliably function and monitor varying biophysical signals even in extreme use scenarios with high humidity or water vapor environments.