Two-dimensional (2D) materials with strictly planar hyper-coordinated motifs are of great importance in fundamental science and potential applications but extremely rare. Here we theoretically design a novel 2D IIB-VIA inorganic system, namely Zn3O2 monolayer, by comprehensive first-principles computations. This Zn3O2 monolayer is composed from highly symmetrical tri-coordinated oxygen and tetra-coordinated zinc, featuring planar and peculiar triangle and pentangle combined bonded network. The newly predicted Zn3O2 monolayer possesses excellent dynamic and thermal stabilities and is also the lowest-energy structure of its 2D space indicated by particle swarm search, supporting its experimentally synthetic viability. A relatively wide band gap of 4.46 eV means it has potential applications in electronics and optoelectronics. The present findings provide a new field of hyper-coordinated 2D nanomaterials for study.