In order to clarify the thermal efficiency of plasma torch under different working parameters, so as to accurately get the real-time energy of plasma jet,and then applying plasma technology to the preparation of aluminum nitride powders and other materials, based on a self-developed plasma torch working with two gas injections, the real-time online thermal efficiency of the proposed plasma torch was monitored by using virtual instrument technology, and the thermal efficiency characteristics was analyzed and discussed. The experimental results show that :1) With a fixed working current, the thermal efficiency increases from 51% to 67% with increasing the main gas injection flow-rate, while it increases first and then decreases with increasing the protective gas injection flow-rate. 2) The thermal efficiency of the proposed plasma torch working with a work current of 70 A is higher about 4% than that at 100 A.