The structure characteristics and the principle of a ventilator are expatiated from 4 aspects including power system, control system, ventilation source, output gas line and components of gas line. The commonality of ventilators in structure is summarized. It is pointed out that with different power systems and control methods, diverse ventilation modes can be assembled based on the commonality of ventilators in structure. In the meantime, according to the structure of ventilator, the common malfunctions are analyzed and the troubleshooting is discussed. It shows that the structure and principle of a ventilator is the basis to solve all problems.