This is a randomized, active-controlled, multicenter phase II clinical trial. The study aims to evaluate the efficacy, safety and tolerability of two different dosing regimens of ASK0912 for Injection compared with Polymyxin B Sulfate for Injection in adult patients with hospital-acquired bacterial pneumonia (HABP) or ventilator-associated bacterial pneumonia (VABP) caused by multidrug-resistant or carbapenem-resistant Gram-negative bacilli. Eligible subjects will be randomly assigned to one of three treatment groups: ASK0912 Regimen 1, ASK0912 Regimen 2, or Polymyxin B Sulfate active comparator group. Subjects will receive assigned intravenous study treatment for 7 to 14 days. The primary efficacy endpoints include clinical cure rate at the Test of Cure (TOC) visit and Day 28 all-cause mortality in the modified intent-to-treat (MITT) population. Safety assessments will be conducted throughout the study to monitor adverse events, laboratory parameters and other safety indicators.