The main frontier problems in hydrology at present are long-term variation of hydrologic time series, spatial distribution and dynamic variation of rainfall, the relationship between a hydrologic phenomenon and the underlying surface, preferential flow, overland flow, scale transformation, equifinality for different parameters, and hydrologic nonlinearity. The scientific content, breakthrough point, and contributions to further development of hydrology are analyzed with regard to these frontier problems in hydrology. These problems should be studied further. More researchers, especially young ones, will be expected to be concerned with, discover, and discuss these frontier problems in hydrology.