Airway pressure release ventilation (APRV) and biphasic positive airway pressure (BIPAP) modes increase mean airway pressure and functional residual capacity by increasing inspiratory time, and allow spontaneous breathing without limitation during high and low airway pressure periods. Many studies confirmed that these two modes can effectively improve ventilation/perfusion and oxygenation in patients with acute respiratory distress syndrome (ARDS). However, APRV/BIPAP modes are not widely used clinically. Several questions have been raised, i.e., why frequent asynchrony occurs between patients and ventilator? Whether augmented spontaneous breathing (ASB) should be used during spontaneous breathing or not? Which kind of ASB is the most effective to decrease the patient’s work of breathing? How do the changes of inspiration/expiration ratio affect the patient-ventilator synchrony and the work of breathing? The APRV/BIPAP mode with inspiratory pressure high/expiratory pressure low settings were 20/8 cmH2O in PB840, G5 and Servo-i. Three different ASB: non, pressure support 16 cmH2O and 100% automatic tube compensation (ATC), combined with five different inspiration/expiration time: 1:5, 2:4, 3:3, 4:2 and 5:1 to formulate 15 test conditions were set on each ventilator. The ASL5000 was used to simulate the lungs of ARDS patients. The computer was connected to the ASL 5000 to collect and analyzed data gained after 10 minutes run of each test conditions according to the settings mentioned above. The purpose of the study was to find the most suitable settings for the three different ventilators, PB840, G5 and Servo-i, with APRV/BIPAP mode and which ventilator has good performance. The results showed that in G5 and Servo-i APRV/BIPAP modes with different ASB, the best patient-ventilator interaction was with pressure support, represented as smallest values of inspiratory time delay (TI delay) and inspiratory trigger pressure (Ptrig). Work of breathing was the least with pressure support, represented as trigger work (WOBtrig) and pressure time product (PTP). In the contrast, the worst and highest of each respectively was with non. However in PB840, we found the highest Ptrig and largest PTP with ATC but the lowest with pressure support. In different inspiration/expiration settings, we found increased WOBtrig, PTP, Ptrig and TI delay with increased inspiration time, possibly due to the spontaneous breathing occurred at high pressure period. The respiratory waveform analysis of 3 ventilators demonstrated that there is no expiratory asynchrony in PB840, probably due to it could automatically shorten its inspiration/expiration time to cooperate the patients breathing cycle. Therefore, PB840 has the best interaction with the simulated lung. Waveform of Servo-i showed irregularity, frequent asynchrony and it could not automatically adjust its inspiration/expiration time to cooperate with the simulated lung. Servo-i has the worst interaction with the simulated lung. In conclusion, expiratory asynchrony occurred in Servo-i and G5. PB840 has longer synchronized interval and it is able to adjust inspiration/expiration time, resulting in better interaction. In the same ventilator we found that without ASB and increased inspiration time would cause poorer patient-ventilator interaction, and increased trigger work. Using pressure support as ASB provides the best interaction and cause the least trigger work.