This paper analyzed the thermal-mechanical performance of the optical-readout bi-material infrared focal array plane (IR-FPA), mainly on the pixel non-uniformity phenomenon. Based on the Fraunhöfer diffraction theory, the model of the initial angle inconformity among the pixels due to the processing bias was presented, the result shows that the initial angle tolerance of pixels must be kept within 0.358° for the 49.5 × 49.5 μm2 pixel. The intensity of the image corresponding to different reflect angles of pixels was tested using the 360° horizontal rotary micro displacement stage driven by stepped motor. And the result agrees with the theoretical calculation. Furthermore, the thermal-mechanic sensitivity S T and dynamic range of the object temperature (blackbody) was also computed, which affords new reference for the research and manufacture of the optical read-out IR-FPA process.