This paper presents the result and analysis of the composition of energy loss occurring in the hydro turbine. Two new types of energy losses,namely the hydraulic loss in the flow channel and the impact loss,are defined. All losses within the hydro turbine are divided into four types and the loss coefficients are defined accordingly. Expressions or characteristic descriptions of these losses as well as the calibration method of the loss coefficients are presented. Furthermore,the torque model of the hydro turbine where the inner energy loss takes place is established. The developed model has been used to calculate the power loss due to the mechanical friction generated by the units’ rotation to solve the difficulty of measurements of the mechanical friction loss in the hydro turbine. The definition of the impact loss explains the phenomenon that the loss of no-load is greater than that of the rated operation. A set of conversion coefficients are defined using the characteristic parameters at the rated operation,which are used to transform the parameters in the torque model into those that are easily measured. Therefore,the expression of the hydro turbine power is converted into a function that has the main servomotor displacement as its single variable. This makes the proposed model be convenient to use. Finally,the proposed model and methods are calibrated and verified using the measured data of a hydropower plant. Good agreement between the modeled results and the measurements indicates that the proposed model can represent the inner energy loss characteristics of the hydro turbine. This paper presents the result and analysis of the composition of energy loss occurring in the hydro turbine. Either two of the energy losses, the hydraulic loss of the flow channel and the impact loss, are defined. into four types and the loss coefficients are defined accordingly. Expressions or special descriptions of these losses as well as the calibration model of the loss coefficients are presented. Furthermore, the torque model of the hydro turbine where the inner energy loss takes place is established. The developed model has been used to calculate the power loss due to the mechanical friction generated by the units’ rotation to solve the difficulty of measurements of the mechanical friction loss in the hydro turbine. The definition of the impact loss explains the phenomenon that the loss of no-load is greater than that of the rated operation. A set of conversion coefficients are defined using the characteristic parame ters at the rated operation, which are used to transform the parameters in the torque model into those that are readily measured. Thus, the expression of the hydro turbine power is converted into a function that has the main servomotor displacement as its single variable. makes the proposed model be convenient to use. The proposed model and methods are calibrated and verified using the measured data of a hydropower plant. Good agreement between the modeled results and the measurements indicates that the proposed model can represent the inner energy loss characteristics of the hydro turbine.