Two-dimensional (2D) materials prepared by a wet-chemical precipitation route exhibit many unique properties and high potential in various fields. Still, simple, rational and green fabrication of target materials remains challenging due to the lack of a guiding principle. Here, we propose a universal qualitative model for 2D materials grown for layered and non-layered crystal structures by wet-chemical precipitation, which is confirmed by both theoretical simulation and experimental results. It demonstrates that 2D growth can be obtained by only tuning reaction concentration and temperature. This model not only has been applied to fabricate more than 30 different 2D nanomaterials in water at room temperature in the absence of additives, but also is promising in optimizing the experimental design of numerous other 2D nanomaterials.