In the process of the laser-matter interaction, when the density of the free electron reaches the damage threshold, the dielectrics will be broken down. Then, the subsequent part of the pulse energy will be strongly absorbed by the laser plasma, the light will be suspended, and this moment is defined as the cut-off time. The cut-off time makes a tremendous impact on the transmission of laser pulse energy. The effects of the input pulse energy on the cut-off time and the cut-off time on the pulse energy transmsstivity are discussed. The corresponding quantitative analysis and simulation are carried out, the simulation results and experimental results fit well. The pulse energy transmissivity is determined by the location of cut-off time. When the distribution of cut-off time at the pulse front edge, on the peak value and at the pulse back edge, the laser pulse energy transmittance will be less than 50%, equal to 50% and greater than 50% respectively. The on-line measurement of the laser pulse energy transmissivity also can be used for online inspection of damage of optical elements.