By the study on accelerated electric ageing characteristics of XLPE cable， the chaotic characteristics of partial discharge pulse waveforms in different ageing stages based on chaos-fractal theory is analyzed and compared. After calculating and comparing wave the correlation dimension and Kolmogorov entropy of pulse waveforms， a conclusion is drawn that partial discharge pulse waveforms of XLPE cable at different electric aging stage have different chaotic characteristics. So a new fault diagnosis method based on chaos-fractal theory for XLPE cable is proposed.