Purpose <p>Due to high spatial resolution, low material budget and good particle identification (PID) performance, drift chamber is an important choice for CEPC trackers. In order to improve the PID capability of drift chambers, an innovative cluster counting method (dN/dx) is proposed.</p> Method <p>Unlike the dE/dx method by measuring the energy loss directly, the dN/dx method measures the number of primary ionizations along the trajectories of particles as they pass through the drift chamber. In this study, a test system with a detector prototype and fast readout electronics was set up and tested with an electron beam. Derivative-based reconstruction algorithm was adopted for the peak finding and clusterization in the signal waveforms.</p> Result <p>The test results show that the mean noise is about 0.9 mV, and the rise time of most peaks is less than 3 ns, which indicates that the system has low noise and high bandwidth, and can be used to accurately measure the ionization signals.</p> Conclusion <p>The preliminary test results have basically validated the feasibility of the dN/dx method.</p>