Abstract: A dynamic analysis technique for the free vibration of generator'S end-winding is presented. The whole paper is composed of two parts. First, it briefly describes the property of rotationally periodical structure and the sector analysis method. Then, to illustrate the use of the above method, its application to the calculation of the nomal modes for three-hundred-thousand-watt turbogenerator's end-winding with inner water-cooled stator and rotor is given.