A nonlinear equation of the modified capacitor model has been solved by means of the Bogoliubov asymptotic method. Dawson only gave a wavebreaking condition which is not complete when it is applied to the inhomogeneous plasma. In this paper, the second wave-breaking condition has been added for completeness; thus the wavebreaking position and wavebreaking time can be uniquely determined simultaneously, and the formulas of the maximum energy of hot electrons and the localized electric field amplitude can also be obtained. The agreement between the theoretical predictions and the experimental results is very good, especially for the wavebreaking time and the maximum energy of the hot electrons.