Abstract: Ageing factors and accelerated life-test methods of class F insulation for stator coils of large turbo-generators are presented, while corresponding accelerated test data of both electrical ageing and generalized thermal ageing summarized and analyzed using Weibull distribution model, and simultaneously relevant characteristic parameters of the life calculation formulae determined by reliability and non-linear regression statistics methods. Based on the life expenditure accumulation theory, an introduction is presented to a life prediction method for simultaneous electrical ageing and generalized thermal ageing of class F insulation for stator coils of turbo-generators, and to the life expenditure assignment scheme for class F insulation of water cooled stator coils. The lower life limit of class F insulation for water cooled stator coils affected mainly by electrical ageing is studied under 2 U_N and 3 U_N conditions. Results show that with above prediction method, the life of class F insulation for stator coils of large turbo-generators can be quantitatively predicted and assessed in the design, manufacture and service stages, thus providing a scientific basis for life determination and extension of relevant insulation in large turbo-generators.