This paper reports an experimental investigation of the dynamic behavior of an axial flow compressor when the flow rate if forced to vary quickly. The results are discussed in two aspects: general trends and special points. Generally, there is a deviation of the dynamic characteristic from the steady-state one, depending upon the algebraic sum of the inertial effect and the lag effect. For the present axial flow compressor, lightly-loaded, the dynamic characteristic goes above the steady-state one while closing the valve and below the steady-state one for opening the valve. Physical explanation is given to the general trend and also to the difference between the behavior of the axial flow compressor and that of the centrifugal compressor. Specifically, the rapid closing of the valve will end up with an operating point end dynamic breaking into the instability limit while the throttle setting is somewhat away from the instability limit position for steady-state operation; and the rapid opening of the valve may produce an initial transient decrease in flow rate thus may have an initial dynamic breaking into the instability limit. Physical explanation is also given to these two special points, which are of great engineering interest with regard to the instability issue.