According to the detection requirement of gas velocity in exhaust pipe of water heater , a kind of detecion device based on venturi effect had been researched. The venturi tube connected to the exhaust pipe of gas water heater, as well as the detection system based on LabVIEW, have been developed. The differential pressure from the venturi tube is detected by integrated silicon micro differential pressure sensor and calibrated in experiment. Compared to the result detected by digital anemometer, it proves the accuracy of the detection device introduced in this paper can meet the application requirements. This research have laid a solid foundation for the future development of gas velocity detector which applied in household appliance, with low cost and high precision.