For measuring the mean flowrate of pulsating gas flow, damping chamber is set between the pulsating source and the flowmeter to damp the pulsating effects. In this paper, the damping chamber is taken as a control volume to derive the basic equations and their dimensionless equations, then, they ale solved by numerical methods to establish criterion equations concerning the relative error and the dimensionless criteria. The results of criterion equations in this paper is superior to that of the theoretical analyses in ISO/TR3313.