Objective To explore the effect of early rehabilitation treatment on complications and prognosis of elderly patients with sever pneumonia undergoing mechanical ventilation. Methods The patients who meeting the inclusion criteria were randomly divided into an early rehabilitation group and a control group, with 35 cases in each group. On basis of same routine treatment, the early rehabilitation group was treated with early rehabilitation. The early rehabilitation methods included exercise therapy, electrical stimulation therapy, swallowing therapy, cough training and wheelchair-bed transfer training, etc. The patients received individual training methods according to their conditions. The difference of two groups were observed in the rates of ICU-acquired weakness (ICU-AW), ventilator-associate pneumonia (VAP), the incidence of delirium, the mechanical ventilation time, ICU-hospital time, total hospital time, 30-day hospital mortality, extubation fail rate and tracheotomy rate. Results Compare with the control group, the incidence of ICU-AW (14.28% vs. 37.14%), VAP (8.57% vs. 28.57%), and delirium (40.00% vs. 65.71%) in the early rehabilitation group were significantly reduced (all P<0.05). The duration of delirium [(3.50±1.31) dvs. (6.40±1.47) d], the ventilation time [(6.32±2.19) d vs. (9.40±4.43) d], ICU hospitalization time [(10.80±3.64) d vs. (15.31±3.85) d] and total hospitalization time [(22.52±7.56) d vs. (30.22±11.54) d] of the early rehabilitation group were significantly lower than the control group (all P<0.001). The tracheotomy rate and 30-day hospital mortality of the early rehabilitation group were significantly lower than the control group (25.71%vs. 51.42% and 28.57% vs. 54.28%, both P<0.05). There was no significant difference in extubation fail rate (5.71%vs. 11.42%, P>0.05). In the early rehabilitation group, there were no complications such as pipe prolapse, limb injury or serious arrhythmia. Conclusion Early rehabilitation can reduce the incidence of ICU-AW, VAP, delirium in elderly patients with severe pneumonia, help to shorten the mechanical ventilation time, ICU hospitalization time and total hospitalization time, reduce extubation failure rate and tracheotomy rate, so it is safe and effective, and worthy of being popularized and applied.