In advanced engineering applications such as aerospace, petrochemical, and rail transportation, bolted joints often operate under complex service conditions involving high temperatures, high pressures, and multi-source coupled loads. Piezoresistive sensors exhibit strong potential for engineering applications owing to their mature fabrication process, low cost, and sensitive response characteristics. In this study, a piezoresistive sensor featuring high-temperature resistance, high integration, and a wide response range was developed. A conductive solution was prepared by mechanically stirring and ultrasonically dispersing carbon black (CB), aluminum oxide (Al₂O₃), and polyamic acid (PAA) solution. The sensor, with a thickness of 100 μm, was fabricated using blade coating followed by thermal imidization, and subsequently integrated with a flexible printed circuit (FPC). Experimental results show that the sensor can operate stably at 300 ℃ for extended periods. In monitoring tests of M20 large-size bolted joints looseness, the sensor demonstrated a torque measurement range of up to 100 N·m and a pressure range of 34.30 MPa. The experimental results verify its stable monitoring performance under high-temperature and high-load conditions, offering a robust technical solution for the identification of loosening states in large-scale bolted joint structures of critical engineering equipment and demonstrating significant potential for practical engineering applications.