The DC FAN cross flow fan 025 has a very complex internal structure. Although the impeller is symmetrical in the circumferential direction, the airflow is asymmetrical, and its relative and absolute velocity fields are unstable. The flowing medium enters the impeller twice, and the flow of the rotor impeller changes continuously along the circumferential direction. On the inner side of one side of the impeller circumference, there is a vortex that can control the flow of the entire airflow, that is, the eccentric vortex of the so-called cross-flow fan. The center of the vortex is somewhere in the inner circumference of the impeller, and it moves along the circumferential direction with the different throttling conditions, and it is the existence of this eccentric vortex that causes the cross-flow. Under certain working conditions, due to the enhanced control force of the eccentric vortex of the cross-flow fan at high speed, the gas in the cross-flow fan cannot be discharged or inhaled normally, and the test system appears abnormal, which is the so-called surge phenomenon.