Liquid metal elastomer has a high permittivity due to the equipotentiality of liquid metal (LM) particles. Introducing a porous structure prepares LM elastomer foam (LMEF) with piezopermittivity, which has a high–stress sensitivity as a stress sensor. However, the random porous structure of LMEF limits the piezopermittivity and the improvement of sensitivity. To solve this problem, a biomimetic LMEF (BLMEF) inspired by the lotus seeds is introduced that has high porosity (>70%), and large permittivity variation (≈5.6). Mechanical and dielectric properties are investigated through finite element analysis and experiments. A flexible capacitive stress sensor is fabricated based on BLMEF. The BLMEF–based stress sensor has high stress sensitivity (2.59 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) and high stability. The sensor can measure human motions, demonstrating potential applications in the field of human motion monitoring. In addition, a smart ergonomic cushion is demonstrated.