As a major gas pollution source in our country, the NOx poses a serious threat to the natural environment and human health. Therefore, it is necessary to develop high-efficiency detection equipment for the in-situ detection of NOx . The emission sources of NOx are mainly industrial exhaust gas and automobile exhaust gas. The gas temperature is relatively high and the composition is relatively complicated. The solid electrolyte-based gas sensor can realize high selectivity and high sensitivity detection of NOx at high temperature. In this study, a Co3O4 / Cr2O3 / YSZ composite material is used as the sensing electrode and YSZ is used as the solid electrolyte to prepare the impedance metric NOx sensor. The sensor is characterized by XRD, SEM and EDX, and the NOx sensing performance at high temperature is systematically studied. Results show that the Co3O4 / Cr2O3 / YSZ sensing electrode with about 200 nm particle size has a high specific surface area due to the loose and porous structure, which is conducive to gas diffusion and mass transfer. The sensor shows a good response-recovery characteristic to NOx, and the O2 concentration has little influence on the sensor. In addition, the sensor shows good reproducibility, stability, and selectivity. To further apply the sensor for the in-situ detection of NOx under high temperature, a novel self-heated sensor is proposed. The sensor shows good sensitivity characteristics, and the concentration detection range is 10×10 -6 ~ 1 500×10 -6 . In addition, the self-heating sensor shows good reproducibility. This study provides a new idea for the in-situ detection of NOx gas at high temperature.