Infrared and night vision optical fusion systems are provided. The first scheme is to add a common-aperture beam splitter in front of the night vision device, which is a band-pass filter having a high transmission for the light with wavelength of 0.78-1 μm, and a high reflectivity for the visible light with wavelength of 0.38-0.78 μm and for the infrared light with wavelength of 8-14 μm. After electrical processing, a target image with a temperature higher or lower than a certain threshold is obtained on the LCD/OLED. The second scheme is to align the night vision objective lens and the infrared objective lens having the same field of view side by side. Since only infrared targets having a temperature above or below a certain threshold are used, white or red humans, animals and vehicles can be clearly seen in a green night vision background with high contrast no matter which scheme is adopted.