Abstract: Theory, apparatus and application of this method are described in this paper. In a laboratory pipe, the air flow rate is measured by this method with a helium tracer. The results are compared with the data got from a standard pitot tube in the same conditions, and the relative error is very small. The above method is also used in Beijing Coking and Chemicals Plant for measuring the inlet coke oven gas flow rate of one large and another medium scale compressors, the systemetic errors of experiment are calculated. It is showed in practice that this tracing method of gas flow rate measurement can be used in the condition which is inavailable for common flow rate measuring instruments. It is disscusscd for further improving the measuring precision.