This paper proposes a method to characterize the spatial electric field distributions of long rod-plane and sphere-plane gaps. The finite element simulation result of the electric field was post-processed， and 66 feature quantities were extracted from the interelectrode path and a conical region. A prediction model was established based on the least squares support vector machine （LS-SVM）， taking the electric field distribution feature set and the discharge voltage as input and output parameters. The improved grey wolf optimizer was used to optimize the model parameters， and the feature dimension was reduced by the maximal information coefficient method. This model was applied to predict the standard switching impulse discharge voltages of long rod-plane and sphere-plane gaps. The results of the case study indicate that the predicted values of test samples are in good agreement with the experimental values， with a maximum relative error of 8.3% and the mean absolute percentage error of 3.2%. This study can provide references for air gap insulation calculation.