Infrared and low-light-level (LLL) images have respective features. Hot targets can be displayed on infrared images. Infrared images are less influenced by actual lighting conditions and bad weathers but have a low contrast. In addition, infrared images are weak in reflecting the details of the targets. The imaging effect of infrared images does not comply with the visual habit of human eyes. LLL images have the features of high definition, rich image slice and compliance with the visual habit of human eyes. However LLL images are greatly disturbed by lighting conditions and weathers. By integrating with respective advantages, the fusion of LLL and infrared images helps to promote the detection and reconnaissance capacities of electro-optical systems. Such fusion is divided into image registration and fusion. The image registration based on calibrated image is adopted to ensure an accurate image registration. The main component analysis method is used for image fusion. After fusion, the details of the images can be displayed more completely and vividly.