Abstract: The 50% breakdown voltage of the air gap is an important basis for the design of external insulation of high voltage power systems.In order to obtain the 50% breakdown voltage of rod-rod air gap under different atmospheric conditions and different gap distances, this paper takes the positive standard switching impulse test data of rod-rod air gap under different meteorological conditions as samples.Based on training set, A breakdown voltage prediction model of rod-rod air gap under different meteorological conditions was established by Bayesian optimization of support vector regression(BOA-SVR).This calculation model takes gap distance, air temperature, air pressure and absolute humidity as input to realize the prediction of 50% breakdown voltage of rod-rod air gap.The results show that the average absolute percentage error of the test samples is 3.3%, which verifies the validity of the SVR to fit the nonlinear relationship between the air gap breakdown voltage and its influencing factors.The model is applied to calculate the breakdown voltage of rod-rod gap under extreme temperature and humidity conditions.The results conform to the objective law.The method can provide reference for the calculation of air gap breakdown voltage under different atmospheric conditions.