Microelectromechanical Systems (MEMS) are evolving and maturing, with advanced technical application and scientific research emerging. Some famous MEMS devices have been mass-produced and commercialized successfully, and the micromirror, for example, is one of the most representative devices. MEMS micromirrors, as the core components of optical scanning system, are used in LiDAR, projection display and other equipments. Compared with traditional discrete scanners, MEMS micromirrors can easily achieve two-dimensional scanning, with the advantages of low energy consumption, small size, and fast response speed, which meet the application needs in various scenarios. Practically, the MEMS micromirror control the light to specific area by specular reflection, and this put forward strict requirements for control accuracy and stability of the device especially in harsh environments. In this context, many studies focus on precise feedback on micromirror angles to achieve closed-loop control. As a high-performance stress gauge, the piezoresistive sensor is successfully integrated into MEMS scanners due to its small size and clear signal. The electromagnetic driven MEMS micromirror integrated with piezoresistive angle sensor is the research object in this paper. The thermal stresses are caused by the thermal expansion or contraction coefficient mismatch of the packaging assembly components. These stresses are the major contributor to lead functional errors or even failure. In order to improve the control precision of MEMS micromirror oscillation amplitude in application, and to reduce the error signal of the integrated piezoresistive angle sensor caused by packaging thermal stress, a stress isolation structure is proposed. When the ambient temperature changes, thermal stress can occur between packaging and device, causing deformation of the MEMS chip. To explore the influence of thermal stress on the output of the piezoresistive angle sensor, a force analysis model is established. On the one hand, according to micromirror’s packaging structure and materials, the structural analysis approach is applied to evaluate the thermal stress and deformation that subjected to the change in temperature. The calculation results show that the thermal stress mainly causes axial deformation and stress of the MEMS chip, and when the temperature changes is 100℃, the deformation is about 12 μm. On the other hand, the output of piezoresistive angle sensor is analyzed and the deduction shows that the axial stress is the main factor leading to the error signal. Based on the above conclusions, a novel packaging stress isolation structure is proposed and tested in experiments. The proposed structure is integrated in form of microspring at corners of the micromirror chip and it is fabricated by original process without consuming extra fabrication. When the thermal stress generates, a significant portion of it can be released through the isolation structure at corners, and the corresponding impact can be reduced greatly. In the experiment, the micromirror chip is attached to the packaging substrate via adhesive, and the substrate is half fixed and half movable. The movable part is connected to translation stage with micrometer to realize precise stretching or contraction, which is set to simulate the deformation load on micromirror chip in a temperature changing environment. Then axial stretching and contraction are loaded to test the performance of devices with or without isolation structure, and the output signals of piezoresistive sensor are compared. The experimental phenomena indicate that under axial stretch and contraction of 12 μm, the angle sensor sensitivity of the traditional chip are 19.22 mV/° and 20.16 mV/° respectively with variation of 0.94 mV/°, appearing divergent trend. Under the same load conditions, the sensitivity of the chip with isolation are 19.37 mV/° and 19.67 mV/° correspondingly, and the variation converge to 0.3 mV/°. The proposed design effectively improves the stability of the angle sensor. In terms of mechanical reliability, the isolation structure passes the shock and vibration test successfully.