METHODS: A randomized, self-controlled and prospective observational study, 20 participants with the severe but stable COPD (FEV1/pre:45.6±2.6%) were recruited. Each subject completed five kinds of tests, on the way to doing treadmill walking exercise as quickly as possible, for a period of 16 days. 5 kinds of tests were included: Test0: baseline without ventilator support. Both Test1 and Test2 were required with the ventilator support (NIPPV via nozzle) in S mode (spontaneous mode) while having a rest: two different pressure levels (IPAP/EPAP:18/8cmH2O and 14/4cmH2O) were in Test1 and Test2 respectively. Test3 and Test4: both exercise and rest were aided with ventilator (NIPPV via total face mask), S mode was applied in Test3, besides, AVAPS-AE (average volume assured pressure support auto-EPAP, AVAPS-AE) mode was adopted in Test4 (parameters:maximum EPAP=8cmH2O, minimum EPAP=4cmH2O, Rate=3cmH2O/min, tidal volume depending on individual BMI). Duration of the walk, distance walked and recovery time were recorded in time. During the exercise sessions, heart rate, respiratory rate, pulse oxygen saturation and Borg score at different time when T1, T2, T3 (the 1st,3rdand 5th minute during walking) and T4, T5, T6 (the 1st, 2nd and 3rd minute during resting) were monitored continuously. These measures above were statistically analyzed.