Abstract: To improve the vacuum environment of an L-band, giga watt-level magnetically insulated line oscillator(MILO), an optimized pumping model was developed for the molecular movement and collision in the high-current vacuum diode chamber and the MILO tube with Monte-Carlo method. According to the three dimensional molecular distributions in MILO, a scheme of distributed pumping was proposed. In this scheme, another pump system which was close to the velvet cathode was introduced and located between the slow wave structure and antenna. Simulation predictions were verified through the experimental test carried out on Torch-01 pulser. Distributed pumping can efficiently reduce the characteristic time of pressure drop to 0.22 times that of single pumping. Moreover, at repetitive operation of MILO, distributed pumping maintains the vacuum degree in MILO better, and for our experimental condition, it can improve the MILOs repetition rate by 5 times.