Venturi tube, EGR flow measuring system and measuring method thereof

The invention discloses a Venturi tube which comprises an inlet segment (11), a contraction segment (18), a throat (12) and a diffusion segment (13); wherein the inlet segment, the contraction segment, the throat and the diffusion segment are successively connected. The Venturi tube further comprises a throat pressure channel (14) which is used for detecting the pressure of the throat (12). The end opening, which extends into the throat (12), of throat pressure channel (14) is located at the connecting position between the throat (12) and the diffusion segment (13). The end opening faces the diffusion segment (13). The Venturi tube provided by the invention can reflect a pressure difference between the throat and the inlet segment through cooperation with the pressure difference sensor, and furthermore can obtain the flowing direction of the fluid which flows through the Venturi tube through a positive pressure difference or a negative pressure difference of the pressure difference sensor, thereby effectively improving a fluid flow measurement accuracy. The invention further provides an EGR flow measuring system with the Venturi tube and a measuring method thereof.