Imaging techniques provide essential information in astronomical and space physics studies. The soft X-ray imager (SXI) will obtain images of the Earth's magnetosphere from solar wind charge exchange emission in a global view. However, it is a challenge to reconstruct its 3D structures from the observed 2D image(s). Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) will have a soft X-ray imager (SXI) onboard, which is a powerful tool to study the geo-space environment under various solar wind conditions.