<p>The jet stability of a DC plasma torch affects not only the service life of the torch but also processing consistency in industrial applications. To evaluate both instantaneous and longstanding jet stabilities of a plasma torch, a novel jet stability evaluation method has been developed in this study. The collected raw signals were first analyzed using the fast Fourier transform and filtered with identified characteristic frequencies. Based on the filtered signals, a 200 ms sliding window method was employed to evaluate the relative fluctuation of arc voltage in terms of both longstanding and instantaneous jet stabilities of the plasma torch. The results show that: (1) the proposed method can effectively evaluate both instantaneous and longstanding jet stability of a DC plasma torch; (2) the arc voltage and arc current signals contain a characteristic frequency, which is strongly influenced by the gas flow rate; (3) the laminar plasma torch operates stably at an arc current of 90&#xa0;A, and its longstanding jet stability improves with increasing gas flow rate. The findings and proposed method provide informative guidance to those interested in the improvement of plasma jet stability and processing consistency.</p>