To address the problem of weak micro-parts vulnerable to interference fit damage in MEMS manufacturing, an interference fit control method for weak micro-parts was studied. The micro-assembly process of the thermomechanical package component (key component in inertial confinement fusion research) was our research topic. First, to address difficulty in detecting deformation of the silicon arm in the assembly process owing to the small assembly space and visual occlusion, a detection method based on gray-scale variations was proposed, and a model of the relationship between gray-scale and deformation was established. Next, to address difficulty in detecting the tiny pose deviation between the silicon arm and the sleeve owing to limited microscopic visual detection accuracy, a qualitative method of judging the pose deviation, based on pressure deformation analysis, is presented. Finally, a quantitative method for assessing the pose deviation was proposed based on gray-scale variations and geometric analysis of parts, completing the overall control strategy design. Experimental results indicated that the proposed method is effective, and thermomechanical package assemblies with interference of 20 µm~26 µm were realized. This method is suitable for interference fit of micro-axis and micro-hole parts in MEMS manufacturing.