The splicing light window has good performance in terms of pneumatic conformality, electromagnetic stealth and large size. However, due to the inconsistent state between the sub-optical windows, the incident wavefronts from the different areas are separated and an additional optical path difference is introduced. Thereby the system Point Spread Function (PSF) is degraded, and the obtained image is blurred. Therefore, analyzing the effect of splicing light window on imaging quality is necessary for the development of high-performance airborne photodetection system. Through the numerical simulation of the image , the factors affecting the optical imaging by the splicing light window are analyzed one by one and the image features and formation causes are determined. At the same time, a design example is given to illustrate the method of reasonably determining the processing precision and surface accuracy of the sub-window.