Abstract: Under the long-term influence of electrical,thermal,mechanical and physical environmental factors,the electrical,mechanical and other performance of power equipment insulation will decline,and there will be aging,damage and other phenomena,which affect the safe and stable operation of power equipment.At present,ultraviolet（UV）detection technology can be applied to detect the early partial discharge of power equipment insulation,and the number of photons detected is greatly affected by the background noise. In order to accurately assess the partial discharge intensity on the insulator surface of transmission line,a method for calculating the discharge spot area was proposed by combining the threshold method and morphological filtering based on the image characteristics of partial discharge on the insulation surface of power equipment and the principle of UV imaging detection. The calculation method was verified by partial discharge test of glass insulator. The experimental results show that with the increase of the external frequency voltage amplitude,the average number of UV photons on the surface of the glass insulator increases,and the area of the discharge spot also increases,which verifies the correctness of the proposed method.