[en] This paper builds up a circuit model of the switch synchronously discharge in the FLTD stage and a circuit simulation model of the FLTD stage. The switch in FLTD simulation model integrates the switch controlled by voltage and self-break switch. The FLTD stage simulation model can simulate stage output influence by switch discharge jitter and bricks discharge each other. The simulation model has been validated by the experiment result of a 14-brick FLTD stage. The influence of the 20-brick FLTD stage output current peak and rise-time with switches discharge synchronously have been simulated by the circuit simulation model of the FLTD. The simulation results indicate that the stage output influence is insignificant when the jitter of switch is less than 5 ns. (authors)