The invention discloses a method for monitoring dirtiness of an insulator. The method comprises the following steps of: arranging an optical fiber on the insulator, connecting the optical fiber with a signal output device and a signal reception measuring and comparing device, removing the external cladding layer from the optical fiber, and determining the insulating dirtiness adhered onto the insulator by a fact that the light intensity in the optical fiber is affected when dirt is adhered to the surface of the optical fiber. According to the method, the insulator is provided with the naked optical fiber of which the skin is peeled off, dirt is adhered to the naked optical fiber in the use of the insulator, and then the light intensity of the optical fiber is affected, so that the insulating dirtiness adhered onto the insulator can be determined by the change of the light intensity. Compared with the existing salt deposit monitoring method, the method has the advantages that the dirtiness condition on the surface of the charged insulator can be directly monitored by light intensity, and the insulating property and the creep distance of the insulator are not affected.