The invention provides a testing device and a testing method of electricity-heat-mechanical stress three-factor combined ageing for transformer paper oil insulation ageing study; the testing device comprises an electric heating ageing oven, in which a transformer paper oil insulation simulator, a shake unit and a temperature control device used for controlling the temperature of the electric heating ageing oven. The shake unit can drive the simulator to vibrate, the simulator is electrically connected with a high-voltage power supply; the testing method includes vacuum drying and oil impregnation of insulating paper, attaching the paper to the earth electrode in a stainless steel case of the testing device, winding coils as a high voltage electrode outside the insulating paper and the earth electrode and injecting insulating oil to the stainless steel case; connecting a high tension lead with the high-voltage power supply and starting the shake unit; sampling the insulating paper and the insulating oil alternately and measuring insulation ageing parameters.