The electronic and mechanical properties of monolayer SnP₂ are calculated by density functional theory (DFT), showing that monolayer SnP₂ is a quasi-direct semiconductor with a moderate bandgap of 1.44 eV. The phonon dispersion, the molecular dynamics and the strain energy reveal that SnP₂ is dynamically, thermally and mechanically stable. Further, the bandgap of SnP₂ sheet can be effectively adjusted by applying strain. These results open the door for future applications in catalysis and optoelectronics.