When the surface pollution of the insulator is cleaned by pulsed laser, the great temperature difference will produce great thermal stress. If the thermal stress is greater than the adhesive force, the pollution layer will fall off. This paper took porcelain insulator and its surface pollution as the object, established the finite element model, analyzed the change law of thermal stress field generated by temperature difference under different energy density, studies the pollution mechanism of pulsed laser cleaning insulator, and determined the optimal cleaning energy density. Also, the cleaning effect has proved by laser experiment.The results show that the first principal stress first presents as compressive stress, which reaches the maximum value at the center of the spot, and the maximum value can reach 1 240 MPa under the condition of ensuring safe cleaning. With the increase of diameter and depth, it is gradually transformed into tensile stress, and the maximum value at 0.014 mm below the center is 105 MPa, where the dirt is removed first. The laser energy density is 2.52 J /cm2~ 3.81 J /cm2, which can realize safe and effective cleaning. The results of this study provide an important basis for the selection of energy density of pulsed laser cleaning porcelain insulator.