The invention discloses a flow guide structure of a ventilating and air supplementing facility of an open flow flood discharge tunnel. An arc flow guide ridge (7) used for guiding air flow to enter the open flow flood discharge tunnel is arranged at the connecting part between a ventilating and air supplementing facility and the open flow flood discharge tunnel (6), the arc length of the arc flowguide ridge is one fourth arc, and the radius of the arc is determined according to the maximum wind speed in the ventilating and air supplementing facility under the maximum flood discharge flow. Theventilating and air supplementing facility and the open flow flood discharge tunnel (6) are connected through the arc flow guide ridge, the flow direction of the air flow at the connecting part between the ventilating and air supplementing facility and the open flow flood discharge tunnel under the condition of high ventilation and wind speed can be smoothed, local position airflow vortexes are eliminated, the ventilating and air supplementing effects of the ventilating and air supplementing facility are improved, and strong noise generated due to the fact that the local air flows in an adverse flow state is avoided, the operation safety of the flood discharge tunnel of the water conservancy project and the production and living environment of workers are guaranteed.