OBJECTIVE: To evaluate the clinical efficacy and safety of Qiguiyin(QGY) formula in patients with severe pneumonia in China compared with a placebo.METHODS: This is a multicenter double-blind, placebo-controlled, randomized clinical trial with two parallel arms. There will be 530 patients enrolled and randomized into either the experimental group(QGY formula) or the control group(placebo). Therapies for patients in the two groups above will be based on the conventional therapy. The primary outcome is 28-day mortality. Secondary outcomes include:(a) duration of hospital stay;(b) duration of time in the intensive care unit(ICU) stays;(c) duration of mechanical ventilation;(d) antibiotic DDD value(which means the doses of antibotics during the treatment period);(e) serum procalcitonin(PCT) level;(f) serum C-reactive protein(CRP)level;(g) Pneumonia severity index(PSI) score;(h)Sequential Organ Failure Assessment(SOFA) score;(i) sputum culture results;(j) blood routine examination results;(k) routine urine test results;(l) stool routine examination results;(m) electrocardiogram results;(n) alanine aminotransferase levels;(o) aspartate amino transferase levels;(p) total bilirubin;(q) creatinine levels;(r) urea nitrogen levels; and(s)adverse events.ETHICS AND DISSEMINATION: The protocol has been approved by the Research Ethics Committee of Beijing Hospital of Traditional Chinese Medicine,Affiliated with Capital Medical University(2018 BL-053-02). This trial aims to provide evidence for QGY formula combined with conventional therapy in treating patients with severe bacterial pneumonia,and to verify the clinical effectiveness and safety of QGY formula in China compared with placebo. Additionally, this trial will reveal the effect of QGY formula on delaying/reversing the characteristics of drug-resistant bacteria.Trial registration number: Chi CTR1800019785.