Aiming at the possible breakdown phenomenon of high power microwave in atmospheric transmission, this paper focuses on the study of the first pulse burst delay and subsequent pulse burst delay in pulse sequences. It is found that the first pulse burst delay is approximately uniformly distributed within the pulse width range, and the subsequent pulse burst delay has a small jitter. The ionization rate is analyzed based on the breakdown delay data, and it is pointed out that under the repeated frequency condition, the initial electron density is high, and the electron density distribution is not suitable for exponential distribution, which makes it impossible to estimate the ionization rate using the standard deviation of the delay data. At the end, the paper proposes a method for calculating ionization rate using repeated frequency pulse burst delay data, and compares the calculated results with the simulation results, which have a good correspondence.