Abstract: The electromagnetic design for Tongnan three-blade bulb type hydro-generator and the main structural design of stator、rotor、 bearing and ventilation cooling system are introduced in this paper.According to the characteristics of the Tongnan hydro-generator, such as low capacity but high voltage level、more poles、large stator diameter、short stator core and so on, the electromagnetic comparison design and structural optimization design are carried out, which solves the problems of electromagnetics load matching and structural stiffness, and provides reference for the design and development of the three-blade bulb type hydro-generator.