In order to assess the insulation condition of transformer accurately, a comprehensive evaluation method is proposed on the basis of the grey matterelement analysis method. First of all, measurement results of insulation parameters and the actual operating condition of transformers are selected as evaluation indices to establish a multiindices evaluation system. Then, the grey matterelements are utilized to quantify eigenvalues of indices and then the condition of transformer more can be evaluated qualitatively and quantitatively. Meanwhile, the independence among indices is taken into account and correlation functions are constructed based on the matterelement theory. The multiindices evaluation problem is then transformed into a singleobjective assessment. However, the correlation between indices would bring duplicate information. To solve this problem, two objective weighting methods, which are the variation coefficient method and the multiple correlation coefficient method, are employed to calculate weights according to the importance of the indices. Finally, the improved method is applied to calculate the degree of grey correlation and the aging level of transformer insulation is evaluated. It is shown that this method is reasonable and feasible.