Abstract: Micro-nano sensors are important devices for data collection and data processing. In this paper, the structure of a rectangular cavity embedded with a triangular metal chip is designed on the side of the waveguide. In addition, the spectral characteristics and sensing applications of the system are simulated by the finite difference time domain method. There are 3-fold Fano resonances appear in the transmission spectrum. Next, we study the physical mechanism of structural resonance based on the electromagnetic field distribution of transmission peaks. It find that Fano resonance occurs when the direction of the electric field in the rectangular cavity is the same as the local field direction of the embedded triangular metal structure. By changing the geometric parameters of the resonant cavity and the embedded chip, the maximum quality factor of the composite cavity is 405. The refractive index sensing properties and temperature sensing properties of the structure are quantitatively analyzed, and the maximum sensing sensitivity of the structure is 2178 nm/RIU, the maximum FOM* is 1.82×10⁶, and the temperature sensitivity is 0.67 nm/℃. The nanostructure of rectangular cavity coupled straight waveguide with embedded triangular metal chip designed in this paper provides ultra-high-Q cavity selection for the research and development of nanosensors in the future.