Abstract: The catchment can be viewed as complex open system.The nonlinear effect in hydrology is closely related to spatial and temporal scale.This paper reviews the research of hydrologic nonlinear effect in hydrology.The nonlinear mechanisms are summarized as follows: (1) the catchment organization patterns; (2) the interaction between water flow and the different subsystem in catchment; (3) the interaction between catchment system and environment; and (4) in different space-time scale level, the dominated factor and process changes.The future simulation development needs to pay attention to the myriad and complexity of catchments again and seek common threads in hydrologic processes.The nonlinear effect and scale effect in hydrology need to be explored further.The hydrology research methods are facing great challenge today.