The invention relates to a composite insulator umbrella skirt surface icing tester and a testing method. A water storage tank is fixedly mounted at the left end of the base. A rotating shaft glass cover is fixedly mounted on the step at the lower surface in a housing. The rotating shaft glass cover is internally provided with an inclination angle adjusting mechanism which is used for adjusting inclination angle of a to-be-tested insulator. The end of the inclination angle adjusting mechanism is provided with a clamping mechanism for clamping an insulator. A bracket on the side surface of the clamping mechanism is provided with an injector device which is used for quantitatively injecting liquid. The injector device is mounted on an injector height adjusting mechanism. The injector device is connected with a transmission mechanism. The bracket at the side surface of the clamping mechanism is also provided with an image photographing device. The tester can be used for researching relationship between composite insulator umbrella skirt surface icing and a surrounding electric field and a surrounding environment, and obtains a corresponding testing result through testing, thereby supplying a testing data for theoretical research for a composite insulator umbrella skirt surface icing mechanism.