Abstract: Measurement of flow rate of flue gas is an important part of pollutant source emission gross monitoring.The key point is how to convert flow rates of single points to the section average value in the continuous monitoring system.This can be resolved through calibrating the continuous monitoring system by reference method,and calculating the velocity field coefficient.The research of calibration of two sets of continuous monitoring systems shows that velocity field coefficient is basically constant.The values are within permissive range during re-verification,and therefore it can be used to calibrate the continuous monitoring system.