A three-pulse time-domain coherent combining system based on the Gires-Tournois interferometer (GTI) cavity is constructed, and the effect of time delay error between phase presetting of pulse burst and amplitude waveform on the combination effect is experimentally studied. When the optical cavity phase control system is in closed-loop state, within the range of 1 ns, changing the clock of the pulse phase presetting voltage with an accuracy of 0.1 ns, the evolution process and laws of the coherent stacking waveform is observed and analyzed. The results show that the clock precise synchronization of the phase and amplitude waveforms of the pulse burst can significantly improve the peak value of the coherent stacked waveform. After experimental optimization, three pulse time-domain coherent combination is achieved, and the ratio of main and secondary pulses achieves 6.43∶1. In addition, if there is a time delay between the phase presetting signal and the amplitude waveform, the stacked waveform will be distorted, and the peak value of the main pulse will decrease relative to the synchronized time.