A flow guiding mechanism with flow channel adjusting function is suitable to a heat dissipating module and an electronic device with an interface card. The flow guiding mechanism includes a supporting component, at least one ventilative structure and a plurality of sheltering components. The interface card is assembled with the supporting component in an assembly direction. The ventilative structure includes a plurality of openings, and the plurality of openings is formed on the supporting component in the assembly direction. The plurality of sheltering components is rotatably disposed on the supporting component. One of the plurality of sheltering components covers a corresponding opening of the plurality of openings while the interface card does not contact the foresaid sheltering component, and the interface card rotates the foresaid sheltering component relative to the supporting component to expose the corresponding opening while the interface card is assembled with the supporting component.