To meet the demands for lightweight and miniaturized satellite remote sensing payloads, based on the theory of primary aberrations in coaxial four-mirror reflective optical systems, an even asphere mirror is used to design a large-field, long-focal-length coaxial four-mirror reflective imaging system. The system has a field of view of ±2.5°, a focal length of 550mm, and a total length of 210mm. The Modulation Transfer Function (MTF) exceeds 0.2 at 100lp/mm, with a maximum distortion of 0.7% within a ±2.5° field of view and 0.27% within a ±1.5° field of view. Compared to traditional coaxial optical systems with a ±1.5° field of view, the monolithic processing of the main four mirrors simplifies assembly and significantly reduces stray light. Comparative analysis shows that, within the same field of view, stray light is reduced by 81% compared to traditional coaxial four-mirror reflective optical systems. This system can reduce design complexity and system weight, providing valuable reference for the design of future satellite remote sensing optical systems.