The class A unidirectional flow hood is a kind of air purifying equipment that provides class A unidirectional flow and creates an environment with high local cleanliness. The working principle is that after passing the high-efficiency filter at a certain air speed, the air is evenly pressed by the damping layer so that the clean air flow is sent to the work area in a unidirectional flow and the flow type and cleanliness required by the work protection area are obtained.