Abstract: The critical flow orifice was used for controlling the airflow in ZZZ-1 ventilation meter. The minimum sectional area of jet throat was calculated through the analysis of the steady flow characteristics of air, the relation-ship between air velocity and passage geometry, and the air velocity and volume passing through the jet, the standard constant flow orifice was determined. The material selection and airflow measurement of the standard constant flow orifice were described. Comparing ZZZ-1 ventilation meter with imported instrument, all performance and technology indexes were in accordance with the industrial standard.