According to the test result about class insulator string of 32 units, a method of calculating 50% ac flashover voltage U50 based on radial basis function network is put forward in this paper. Inputs of the model are equivalent salt deposit density ρESDD and nonsoluble deposit density ρNSDD ,the output of the model is 50% ac flashover voltage of polluted insulator strings, the Orthogonal least squares algorithm was used to select right hide layer neurons and center vectors, and the weight from hide layer neurons to output layer neurons are determined by pseud-inverse method. The calculating result is in concordance with the test result, it is indicated that the model can give some references to access the pollution condition of external insulation.
