The invention discloses a judgment method for the ageing degree of composite insulator silicon rubber. The judgment method comprises the following steps: S1, cutting a test sample from a silicon rubber umbrella skirt of a composite insulator to be detected; carrying out X-ray photoelectron energy spectrum analysis on the test sample to obtain a Si 2p energy spectrum of the test sample; S2, carrying out peak-differentiating and fitting processing on the Si 2p energy spectrum obtained by S1 by utilizing a peak-differentiating and fitting method, so as to obtain four sub-peaks corresponding to silicon-oxygen functional groups with four structures of a Si atom in the silicon rubber umbrella skirt; S3, calculating the peak area of each sub-peak, and determining the relative ratio of the silicon-oxygen functional groups of all the structures by the ratio of the peak areas of all the sub-peaks; S4, calculating an average O atom number around one Si atom according to the relative ratio of thesilicon-oxygen functional groups of all the structures obtained by S3; S5, judging the ageing degree of the silicon rubber in the test sample according to the average O atom number. The judgment method can be used for relatively accurately judging the ageing degree of the composite insulator silicon rubber.