<p>During geothermal energy extraction, soil–structure interfaces in energy geostructures undergo complex thermo–hydro–mechanical (THM) interactions, yet dedicated experimental apparatus remains lacking. To address this gap, a novel non-isothermal unsaturated soil–structure interface testing apparatus was independently developed. The apparatus adopts PID closed-loop temperature control, enabling direct regulation of interface temperature and heating/cooling rates, thereby ensuring superior thermal uniformity and accuracy during the experiment compared with conventional indirect methods. It integrates suction regulation, stress- and displacement-controlled loading, monotonic and cyclic shear testing, and multiple normal boundary conditions, including constant normal load (CNL), constant normal stiffness (CNS), and constant normal height (CNH), within a single platform. This integrated configuration provides a more comprehensive experimental capability and offers a novel approach for investigating the THM behavior of soil–structure interfaces. Modular expansion and secondary software development further enhance the versatility of the apparatus. Structural refinements, including optimized sensor placement, roller-ball clearance, and sliding block isolation, minimize the influence of frame deformation and friction on measurement accuracy. Calibration procedures, testing protocols, and preliminary test results are presented and thoroughly discussed. Preliminary experimental outcomes have effectively demonstrated the reliability and accuracy of the developed apparatus. The research findings provide critical technical support for further investigations into the mechanical properties of non-isothermal unsaturated soil–structure interfaces and for validating related constitutive models.</p>