As a derivative of the two-dimensional material family, two-dimensional Janus materials have garnered widespread attention in recent years. Consequently, in this work, we systematically investigated the stability, electronic properties, photocatalytic properties, optical properties, and carrier mobility of SPtAZ 2 (A = Si and Ge; Z = N, P, and As) monolayers using first-principles calculations. In the equilibrium state, we identified four stable structures that exhibited the properties of indirect band gap semiconductors using the HSE06 hybrid functional. Through the exploration of the photocatalytic and optical properties of these four stable structures, we observed that SPtSiN 2 , SPtSiP 2 , and SPtGeAs 2 monolayers possess favorable band edge positions, high solar-to-hydrogen efficiency (up to 30.74%), and light absorption efficiency, thus endowing these three structures with commendable photocatalytic and light absorption performance. We additionally calculated the carrier mobility of these three structures and identified significant differences in electron and hole mobilities in the same direction, facilitating the effective separation of electrons and holes. Finally, we explored the effects of biaxial strain on the electronic properties, photocatalysis, and light absorption of stable SPtAZ 2 monolayers. Our research results not only expand the 2D Janus material family, but also successfully predict a type of photocatalyst capable of utilizing visible light for overall water splitting.