Abstract: As more low-head hydro resource is developed, the proportion of tubular turbine units in China is gradually increasing. But for all these units, their inertia time constants and inertia ratios usually fall far beyond the required scope of control systems by the current national standard of hydro turbines due to the limits of their application conditions and structures, particularly their overlarge constants of water inertia time and too small constants of unit inertia time. This paper compares the application conditions of the hydro turbine control systems specified in the domestic and overseas standards, analyzes our survey data on the parameters and operation conditions of the existing typical power plants in China, and examines the stable domain and regulation quality using a mathematical model of hydro turbine control systems. The results show that all these existing low-head tubular turbine units still have large stability domains and can operate under safe and reliable conditions. We can demonstrate that better regulation quality can be obtained as long as the control parameters are adjusted properly, and that the required tuning of turbine unit parameters stays within the normal ranges recommended by IEC. Thus we suggest that the requirement of the unit inertia ratio in the standard be revised to be no more than 1.5 and the requirement of the unit inertia time constant no less than 1.5 sec.