Scanning microlens array systems can effectively resolve the contradiction between small strokes and large fields of view using micromotion scanning imaging. They generally adopt the Keplerian telescope structure and perform field-of-view scanning through the relative lateral displacement of the lenses. In this paper, we propose a four-piece microlens array based on the Keplerian telescope structure and evaluate the effect of the angular magnification of the microlens array on the scanning microlens array system in the 3?5 μm band. When the angular magnification is less than 1, more stray light is generated after crosstalk and the upper limit of the energy utilization of the system is limited, resulting in a restricted diffraction limit. Higher angular magnifications increase the upper limit of energy utilization. When the angular magnification is changed from 0.67× to 0.83×, the energy utilization increases from 43% to 69%. When the angular magnification is greater than 1, the energy utilization of the system is no longer limited by the structure, and the structure with an angular magnification of 1.5× is optimized under the condition of suppressing crosstalk. The results of the image quality evaluation are as follows: the RMS radius of each scanning field reaches the pixel size of the detector, and the MTF reaches 0.6@17l p/mm. As a parameter characterizing the structure of the microlens array, the angular magnification is related to the energy utilization of the system, which affects the image quality. Therefore, the analysis and study of angular magnification can provide a basis for the design and implementation of the scanning microlens array system.