Abstract: The propagation and evolution of streamer under repetitive nanosecond pulses(RNP) is significantly different from that under single pulse. In view of the differences in the physical processes and time scales involved in the pulse period and interval period, this paper adopts a global-particle coupling method to simulate streamer discharge under continuous pulses in nitrogen at atmospheric pressure, and the interval time is 1 ms. The study reveals that, during the first pulse period, a transition from inception cloud to streamer occurs. The number density of remaining free electrons in the first interval is always on the same order of magnitude as the positive space charge, which is significantly higher than the negative space charge. Therefore, the negative ions in the remaining charged particles can be ignored in the initial condition setting of the subsequent pulse period. In the second and third pulse periods, the discharge channel presents a three-stage ionization mode of 1) initial cloud; 2) discharge channel fusion; 3) rapid breakdown.