Abstract: Herein, we reported the transition technique from extreme high vacuum, 1×10^-9 Pa, in the beam extraction line of booster ring (BRing) to ultrahigh vacuum, 5×10^-7 Pa, in fragment separator of High Intensity Heavy-Ion Accelerator Facility. The original work included the fast-closing valve and non-evaporable getter pump, installed in the middle between the baked and unbaked segments of 66 m long BRing beam extraction line. The influence of the fast-closing valve on the pressure distributions in the baked/unbaked segments separately pumped was mathematically modeled, numerically simulated with VAKTRAK software, and experimentally evaluated. The simulated results show that the transition from 1×10^-9 to 5×10^-7 Pa can be routinely and reliably performed. The simulated and measured results were in good agreement. In addition, the fast closing valve is capable of protecting the whole vacuum system against any accidental collapse.