The invention provides an IEC61850-based digital water turbine speed control system which digitally controls a water turbine through three network layers, i.e. a station monitor and control layer, a bay layer and a process layer. A main body of the water turbine speed control system is distributed on the bay layer and the process layer, and a water turbine controller is arranged on the bay layer; an intelligent hydraulic servo system, a unit merging unit, a system merging unit, an intelligent pressure oil system, an intelligent tachometric relay and a unit intelligent unit are arranged in the process layer; the water turbine controller and intelligent electronic equipment which is arranged on the station monitor and control layer and the bay layer form a redundant high-speed star Ethernet which is a bay layer Ethernet; the water turbine controller and intelligent electronic equipment which is arranged on the process layer form a redundant high-speed star Ethernet structure which is a process layer Ethernet; the communication protocol of each intelligent electronic equipment meets the IEC61850 standard requirement; and the water turbine controller receives various instructions and sets through the Ethernet and collects relevant information, thereby realizing the frequency modulation, phase modulation and power modulation of a unit.