The consolidated differential protection could not be installed in generator in many old hydraulic power plants they are in running. Affected by various factors, the mal-operation of turn-to-turn protection based on other principles occurs easily. For a long time in operating the power plant, to prevent the mal-operation of turn-to-turn protection is a key point, so the turn-to-turn protection in actual operation is often ineffective. For large multi-polar hydraulic generator, if the turn-to-turn protection failed to operate, it will produce incalculable damage. It is so quite important to simulate before installing the main protection in new generating-sets. For the generators have not been simulated, this paper proposes a new simple setting method, which uses stator winding spreading figure to analyze the potential circle number of upper and lower stator bars in the same lot of same phase. It is of more practical value than both setting according to “Guideline” and setting blindly. From the analysis about the stator structure, turn-to-turn protection configuration, setting and operation history of 11 representative large hydraulic generators along the Qingjing River Valley, it can be drawn that turn-to-turn protection of old generating-sets is almost out of work which is installed before 2001 and the sensitivity of 17.5% new generating-sets put into operation by 2007 can't be guaranteed. It also indicates that excitation system impact considerably on main protection of generator. This paper discusses the turn-to-turn protection of large hydraulic generator.