Utilizing the ab inito calculation, we focus on exploring the mechanical behaviors and optoelectronics characteristics of the Janus SiSSe monolayer. First, a dynamic stability test was performed, and the results showed the system was completely stable. The obtained results show that the Janus SiSSe monolayer has small elastic constants and a good load-bearing capacity. Through hybrid functional calculations, the energy band structures of the Janus SiSSe have been explored and show the properties of the semiconductor material. Under mechanical strains, energy band structures and the bandgap energy have significantly changed, with a maximum increase of ~ 32% and a maximum decrease of ~ 53% compared to the natural state. Besides, we also have investigated the absorption spectrum under mechanical strains. Vertical strain leads to a maximum improvement of ~ 3.5 times compared to the natural state. The findings provide helpful information and are practical for the application of the Janus SiSSe in nanoelectronics and optical devices.