<p>The variation law of resistivity of composite materials under multiphysics field coupling conditions is crucial for their application in extreme environments, but there is still a lack of systematic research at present. This paper studies the evolution law of resistivity of quartz fiber reinforced silica composites under the multi-field coupling action of electric field, temperature, pressure, and humidity through the method of combining experiments and simulations. A multi-field coupled resistivity model was proposed, combining the Arrhenius thermal activation model, the Poole–Frenkel effect, and the exponential relationship related to humidity/pressure. The multiphysics field simulation results demonstrate that under the coupled influence of the composite external field, the alteration in carrier dynamics and the refinement of the material’s microstructure act synergistically to induce a qualitative transformation of the conductive network, resulting in an exponential reduction in electrical resistivity.Experimental verification was carried out through the self-designed multi-field coupling resistivity test system. It was found that the synergistic effect of pressure and temperature (<i>P</i> &gt; 2 × 10⁵&#xa0;Pa, <i>T</i> &gt; 500&#xa0;K) could reduce the resistivity by 2 to 3 orders of magnitude. Weight analysis based on XGBoost machine learning indicates that pressure (60.9%) has the greatest impact on resistivity, followed by electric field (22.5%), temperature (13.7%), and humidity (2.9%). This research provides a theoretical basis and experimental support for the resistivity regulation of composite materials in extreme environments in fields such as aerospace and energy.</p> Graphical Abstract <p></p>