The invention discloses a negative pressure air drafting hood. The negative pressure air drafting hood can be used at the tail end of a negative pressure air system. The negative pressure air drafting hood is a hollow hood which gradually changes from a circular truncated cone to a square from the upper end to the lower end, and an upper and lower bi-spherical pore plate combination structure is arranged in a center region in the air drafting hood and is fixed onto the inner wall of the air drafting hood through two wing-shaped structures. When the negative pressure air drafting hood is used for negative presusre air drafting, the upper and lower bi-spherical pore plate combination structure realizes even air speed and constant air pressure of the horizontal cross section at the air drafting opening position of the air drafting hood.