The invention discloses a fusion system for infrared images and low-illumination images. The fusion system comprises a low-illumination optical lens group, an infrared optical lens group, a synchronous focus control device, a low-illumination image sensor, an infrared image sensor, a low-illumination image sensor driving module, an infrared image sensor driving module, an image sensor simulation front end, a low-illumination image signal processor, an infrared image signal processor, a synchronous signal generator, a synchronous image collection module, a digital image processing module, an image display control module, a microdisplay, a display magnifying lens group, a power supply module, a processor peripheral circuit and a display switching key. According to the fusion system, two-way synchronous focus control of an infrared and low-illumination video is realized optically, and complexity of a back-end registration algorithm is reduced; with the adoption of an embedded type multicore heterogeneous processor, performance of image collection control and real-time algorithm treatment is guaranteed; three-type display switching of infrared, low-illumination and pseudo-color fusion video can be realized.