Abstract: An out flow resistance switching ventilator and its methodology for providing mechanical ventilation support to the respiratory failure patient are claimed. Based on the continuous out flow impounding ventilation mechanism, the apparatus provides ventilation by switching flow resistance between two different levels at a continuous gas flow system outlet valve controlled by patient's spontaneous breathing or preset mandatory parameters, resulting in airway pressure levels switching, and therefore creating lung volume switching, which is totally different from either volume ventilation or pressure ventilation mechanism utilized in the current conventional ventilators.